PyMailGUI, Version 3.0

May, 2010 (2.1 January, 2006)
Programming Python, 4th Edition
Mark Lutz, for O'Reilly Media, Inc.

PyMailGUI is a multiwindow interface for processing email, both online and offline. Its main interfaces include one list window for the mail server, zero or more list windows for mail save files, and multiple view windows for composing or viewing emails selected in a list window. On startup, the main (server) list window appears first, but no mail server connection is attempted until a Load or message send request. All PyMailGUI windows may be resized, which is especially useful in list windows to see additional columns.

Note: To use PyMailGUI to read and write email of your own, you must change the POP and SMTP server names and login details in the file, located in PyMailGUI's source-code directory. See section 12 for details.


  1. Version Enhancements
  2. List Window Actions
  3. View Window Actions
  4. Offline Processing
  5. Viewing Text and Attachments
  6. Sending Text and Attachments
  7. Mail Transfer Overlap
  8. Mail Deletion
  9. Inbox Message Number Synchronization
  10. Loading Email
  11. Unicode and Internationalization Support
  12. The mailconfig Configuration Module
  13. Dependencies
  14. Miscellaneous Hints ("Cheat Sheet")

Version Enhancements

The following lists major enhancements in recent version.

Version 3.0 enhancements

Version 2.1 enhancements

Version 2.0 enhancements

List Window Actions

Click list window buttons to process email:

Double-click on an email in a list window's listbox to view the mail's raw text, including any mail headers not shown by the View button. List windows opened for mail save files support all of the above except Load. After the initial Load, Load only fetches newly arrived message headers. To forceably reload all mails from the server, restart PyMailGUI. There is reload button, because full reloads are only required on rare deletion and inbox synchronization errors (described ahead), and reloads are initiated automatically in these cases.

Click on emails in the main window's listbox to select them. Click the "All" checkbox to select all or no emails at once. More than one email may be selected at the same time: View, Delete, Reply, Fwd, and Save buttons are applied to all currently selected emails, in both server and save-file list windows. Use Ctrl+click to select multiple mails, Shift+click to select all from prior selecion, or click+move to drag the selection out.

In 2.1, most of the actions in the server List window automatically run a quick-check to detect inbox out-of-synch errors with the server. If a synch error pop up appears, a full index reload will be automatically run; there is no need to stop and restart PyMailGUI (see ahead in this help).

View Window Actions

Action buttons in message view windows (View):

Actions in message compose windows (Write, Reply, Fwd):

Parts and Split buttons appear in all View windows; for simple messages, the sole part is the message body. Message reply, forward, and delete requests are made in the list windows, not message view windows. Deletions do not erase open view windows.

New in 2.1: View windows also have up to a fixed maximum number of quick access buttons for attached message parts. They are alternatives to Split. After the maximum number, a '...' button is added, which simply runs Split. The maximum number of part buttons to display per view window can be set in the user settings module (described ahead).

Offline Processing

To process email offline: Load from the server, Save to a local file, and later select Open to open a save file's list window in either the server List window or another save file's List window. Open creates a new List window for the file, or raises its window if the file is already open.

A save file's list window allows all main window actions listed above, except for Load. For example, saved messages can be viewed, deleted, replied to, or forwarded, from the file's list window. Operations are mapped to the local mail save file, instead of the server's inbox. Saved messages may also be saved: to move mails from one save file to another, Save and then Delete from the source file's window.

You do not need to connect to a server to process save files offline: click the Open button in the main list window. In a save-file list window, a Quit erases that window only; a Delete removes the message from the local save file, not from a server. Save-file list windows are automatically updated when new mails are saved to the corresponding file anywhere in the GUI. The sent-mail file may also be opened and processed as a normal save-mail file, with Open.

Note that Save buttons in list windows save the full message text (including its headers, and a message separator). To save just the main text part of a message being viewed or composed, either use the Save button in the text editor component at the bottom of a view or edit window, or select the "Split" action button of view windows. Saves in the text editor component can be useful to save a draft of the mail being composed to a temporary file; it can later be pasted into a compose window if needed. To save attachments, see the next section.

New in 2.1: local save-file Open and Delete requests are threaded to avoid blocking the GUI during loads and deletes of large files. Because of this, a loaded file's index may not appear in its List window immediately. Similarly, when new mails are saved or messages are sent, there may be a delay before the corresponding local file's List window is updated, if it is currently open.

As a status indication, the window's title changes to "Loading..." on loads and "Deleting..." during deletes, and is reset to the file's name after the thread exits (the server window uses pop ups for status indication, because the delay is longer, and there is progress to display). Eventually, either the index will appear and its window raised, or an error message will pop up. Save-file loads and deletes are not allowed to overlap with each other for a given file, but may overlap with server transfers and operations on other open files.

Note: save-file Save operations are still not threaded, and may pause the GUI momentarily when saving very many large mails. This is normaly not noticeable, because unlike Open and Delete, saves simply append to the save-file, and do not reload its content. To avoid pauses completely, though, don't save very many large mails in a single operation.

Also note: the current implementation loads the entire save-mail file into memory when opened. Because of this, save-mail files are limited in size, depending upon your computer. To avoid consuming too much memory, you should try to keep your save files relatively small (at the least, smaller than your computer's available memory). As a rule of thumb, organize your saved mails by categories into many small files, instead of a few large files.

Viewing Text and Attachments

PyMailGUI's view windows use a text-oriented display. When a mail is viewed, its main text is displayed in the View window. This text is taken from the entire body of a simple message, or the first text part of a multipart MIME message. To extract the main message text, PyMailGUI looks for plain text, then HTML, and then text of any other kind. If no such text content is found, nothing is displayed in the view window, but parts may be opened manually with the "Split" button (and quick-access part buttons in 2.1, described below).

If the body of a simple message is HTML type, or a HTML part is used as the main message text, a web browser is popped up as an alternative display for the main message text, if verified by the user (the mailconfig module can be used to bypass the verification; see ahead). This is equivalent to opening the HTML part with the "Split" button, but is initiated automatically for the main message text's HTML. If a simple message is something other than text or HTML, its content must be openened manually with Split.

When viewing mails, messages with multipart attachments are prefixed with a "*" in list windows. "Parts" and "Split" buttons appear in all View windows. Message parts are defined as follows:

In both cases, message parts may be saved and opened with the "Split" button. For simple messages, the message body may be saved with Split, as well as the Save button in the view window's text editor. To process multipart messages:

For "Split", select a local directory to save parts to. After the save, text parts open in the TextEditor GUI, HTML and multimedia types open in a web browser, and common Windows document types (e.g., .doc and .xls files) open via the Windows registry entry for the filename extension. For safety, unknown types and executable program parts are never run automatically; even Python programs are displayed as source text only (save the code to run manually).

Web browsers on some platforms may open multimedia types (image, audio, video) in specific content handler programs (e.g., MediaPlayer, image viewers). No other types of attachments are ever opened, and attachments are never opened without user verification (or authorization in 2.1, described below). Browse the parts save directory to open other parts manually.

To avoid scrolling for very long lines (sometimes sent by HTML-based mailers), the main text part of a message is automatically wrapped for easy viewing. Long lines are split up at the first delimiter found before a fixed column, when viewed, replied, or forwarded. The wrapping column may be configured or disabled in the mailconfig module (see ahead). Text lines are never automatically wrapped when sent; users or recipients should manage line length in composed mails.

New in 2.1: View windows also have up to a fixed maximum number of quick-access buttons for attached message parts. They are alternatives to Split: selecting an attachment's button automatically extracts, saves, and opens that single attachment directly, without Split directory and pop-up dialogs (a temporary directory is used). The maximum number of part buttons to display per view window can be set in the user settings module (described ahead). For mails with more than the maximum number of attachments, a '...' button is added which simply runs Split to save and open any additional attachments.

Also in 2.1, two settings in the module (see section 10) can be used to control how PyMailGUI opens parts in the GUI:

Both are used for View window Split actions and part quick-access buttons. If okayToOpenParts is False, quick-access part buttons will not appear in the GUI, and Split saves parts in a directory but does not open them. verifyPartOpens is used by both Split and quick-access part buttons: if False, part buttons open parts immediately, and Split opens all known-type parts automatically after they are saved (unknown types and executables are never opened).

An additional setting in this module, verifyHTMLTextOpen, controls verification of opening a web browser on a HTML main text part of a message; if False, the web browser is opened without prompts. This is a separate setting from verifyPartOpens, because this is more automatic than part opens, and some HTML main text parts may have dubious content (e.g., images, ads).

Sending Text and Attachments

To compose an email, use the composition view window to enter its headers, add and edit its main message text, and add any attachments. Message text is edited in the PyEdit component at the bottom of the window; use its Save button to save a draft of your mail's text to a temporary file if desired, from which it may be copied and pasted later (see "Offline Processing" for more on saves).

When composing new mails, the view window's "Attach" button adds selected files as attachments, to be sent with the email's main text when the View window's "Send" is clicked. Attachment files may be of any type; they are selected in a pop-up dialog, but are not loaded until Send. The view window's "Parts" button displays attachments already added.

The main text of the message (in the view window editor) is sent as a simple message if there are no attachments, or as the first part of a multipart MIME message if there are. In both cases, the main message text is always sent as plain text. HTML files may be attached to the message, but there is no support for text-or-HTML multipart alternative format for the main text, nor for sending the main text as HTML only. Not all clients can handle HTML, and PyMailGUI's text-based view windows have no HTML editing tools.

Multipart nesting is never applied: composed mails are always either a simple body, or a linear list of parts containing the main message text and attachment files.

For mail replies and forwards, headers are given intial values, the main message text (described in the prior section) is wrapped and quoted with '>' prefixes, and any attachments in the original message are stripped. Only new attachments added are sent with the message.

To send to multiple addresses, separate each recipient's address in To and Cc fields with commas. For instance:, "Smith, Bob" <>,

Note that commas can appear both as address separators as well as embedded in address name components. Because these are fully parsed when split, it's okay to use commas in both contexts in recipient lists. For replies, this is handled automatically: the To field is prefilled with From sender in the original message, and the Cc field is prefilled with all unique original mail recipient addresses less the new sender. Cc and Bcc headers fields are ignored if they contain just the initial "?" when sent.

All addresses listed in To, Cc,and Bcc headers are sent the composed mail message. To and CC headers are sent in the message itself, but the Bcc header is not: its content is used only to name recipients, not to generate a mail header line (that's the main point of a blind copy). Technically, Bcc is used for the mail envelope, but not the message text. The Bcc line is not enabled by default, but can be enabled in the mailconfig module; as a convenience, it is prefilled to the sender's addrress, since this is a common use case (simply delete this text to Bcc to others). Duplicate email addresses are removed from the recipients list before mail is sent. Windows users: Ctrl-C and Ctrl-V work to copy and paste text in header entry fields.

Successfully sent messages are saved in a local file whose name you list in the module. Sent mails are saved if the variable "sentmailfile" is set to a valid filename; set to an empty string to disable saves. This file may be opened using the Open button of the GUI's list windows, and its content may be viewed, processed, deleted, saved, and so on within the GUI, just like a manually saved mail file. Also like manually saved mail files, the sent-file list window is automatically updated whenever a new message is sent, if it is open (there is no need to close and reopen to see new sends). If this file grows too large to open, you can delete its content with Delete, after possibly saving sent mails you wish to keep to another file with Save.

Note that some ISPs may require that you be connected to their systems in order to use their SMTP servers (sending through your dial-up ISP's server while connected to a broadband provider may not work--try the SMTP server at your broadband provider instead), and some SMTP servers may require authentication (set the "smtpuser" variable in the module to force authentication logins on sends). See also the Python library module smptd for SMTP server tools; in principle, you could run your own SMTP server locally on 'localhost'.

Mail Transfer Overlap

PyMailGUI runs mail server transfers (loads, sends, and deletes) in threads, to avoid blocking the GUI. Transfers never block the GUI's windows, and windows do not generally block other windows. Users can view, create, and process mails while server transfers are in progress. The transfers run in the background, while the GUI remains active.

PyMailGUI also allows mail transfer threads to overlap in time. In particular, new emails may be written and sent while a load or send is in progress, and mail loads may overlap with sends and other mail loads already in progress. For example, while waiting for a download of mail headers or a large message, you can open a new Write window, compose a message, and send it; the send will overlap with the load currently in progress. You may also load another mail, while the load of a large mail is in progress.

While mail transfers are in progress, pop-up windows display their current progress as a message counter. When sending a message, the original edit View window is popped back up automatically on Send failures, to save or retry. Because delete operations may change POP message numbers on the server, this operation disables other deletions and loads while in progress.

Offline mail save-file loads and deletes are also threaded: these threads may overlap in time with server transfers, and with operations on other open save files. Saves are disabled if the source or target file is busy with a load or save operation. Quit is never allowed while any thread is busy.

Version 3.0 update: if a message's fetch is in progress, it prevents any new fetch requests that it is a part of, until its fetch completes. This avoids fetching the same message twice, in parallel (a safe, but pointless action). Other fetches can process in parallel freely if disjoint.

Mail Deletion

Mail is not removed from POP servers on Load requests, but only on explicit "Delete" button deletion requests, if verified by the user. Delete requests are run immediately, upon user verification.

To delete your mail from a server and process offline: in the server list window select the All checkbutton, Save to a local file, and then Delete to delete all mails from the server; use Open to open the save file later to view and process saved mail.

When deleting from the server window, the mail list (and any already viewed message text) is not reloaded from server, if the delete was successful. If the delete fails, all email must be reloaded, because some POP message numbers may have changed; the reload occurs automatically. Delete in a file list window deletes from the loal file only.

As of version 2.1, PyMailGUI automatically matches messages selected for deletion with their headers on the mail server, to ensure that the correct mail is deleted. If the mail index is out of synch with the server, mails that do not match the server are not deleted, since their POP message numbers are no longer accurate. In this event, an error is displayed, and a full reload of the mail index list is automatically performed; you do not need to stop and restart PyMailGUI to reload the index list. This can slow deletions (it adds roughly one second per deleted mail on the test machine used), but prevents the wrong mail from being deleted. See the POP message number synchronization errors description in the next section.

Inbox Message Number Synchronization

PyMailGUI does header matching in order to ensure that deletions only delete the correct messages, and periodically detect synchronization errors with the server. If a synchronization error message appears, the operation is cancelled, and a full index reload from the server is automatically performed. You need not stop and restart PyMailGUI and reload the index, but must reattempt the operation after the reload.

The POP email protocol assigns emails a relative message number, reflecting their position in your inbox. In the server List window, PyMailGUI loads its mail index list on demand from the server, and assumes it reflects the content of your inbox from that point on. A message's position in the index list is used as its POP relative message number for later loads and deletes.

This normally works well, since newly arrived emails are added to the end of the inbox. However, the message numbers of the index list can become out of synch with the server in two ways:

  1. Because delete operations change POP relative message numbers in the inbox, deleting messages in another email client (even another PyMailGUI instance) while the PyMailGUI server list window is open can invalidate PyMailGUI's message index numbers. In this case, the index list window may be arbitrarily out of synch with the inbox on the server.

  2. It is also possible that your ISP may automatically delete emails from your inbox at any time, making PyMailGUI's email list out of synch with message numbers on the mail server. For example, some ISPs may automatically move an email from the inbox to the undeliverable box, in response to a fetch failure. If this happens, PyMailGUI's message numbers will be off by one, according to the server's inbox.

To accommodate such cases, PyMailGUI 2.1 always matches messages to be deleted against the server's inbox, by comparing already fetched headers text with the headers text returned for the same message number; the delete only occurs if the two match. In addition, PyMailGUI runs a quick check for out-of-synch errors by comparing headers for just the last message in the index, whenever the index list is updated, and whenever full messages are fetched.

This header matching adds a slight overhead to deletes, index loads, and mail fetches, but guarantees that deletes will not remove the wrong message, and ensures that the message you receive corresponds to the item selected in the server index List window. The synch test overhead is one second or less on test machines used - it requires 1 POP server connect and an inbox size and (possibly) header text fetch.

In general, you still shouldn't delete messages in PyMailGUI while running a different email client, or that client's message numbers may become confused unless it has simlar synchronization tests. If you receive a synch error pop up on deletes or loads, PyMailGUI automatically begins a full reload of the mail index list displayed in the server List window.

Loading Email

To save time, Load requests only fetch mail headers, not entire messages. View operations fetch the entire message, unless it has been previously viewed (already loaded messages are cached). Multiple message downloads may overlap in time, and may overlap with message editing and sends.

In addition, after the initial load, new Load requests only fetch headers of newly arrived messages. All headers must be refetched after a delete failure, however, due to possibly changed POP message numbers.

PyMailGUI only is connected to a mail server while a load, send, or delete operation is in progress. It does not connect at all unless one of these operations is attempted, and disconnects as soon as the operation finishes. You do not need any Internet connectivity to run PyMailGUI unless you attempt one of these operations. In addition, you may disconnect from the Internet when they are not in progress, without having to stop the GUI--the program will reconnect on the next transfer operation.

Note: if your POP mail server does support the TOP command for fetching mail headers (most do), see variable "srvrHasTop" in the module to force full message downloads.

Also note that, although PyMailGUI only fetches message headers initially if your email server supports TOP (and has a faster GUI actions queue in 3.0), this initial fetch can still take some time for very large inboxes; as a rule of thumb, use save-mail files and deletions to keep your inbox small.

3.0 Update: to address the prior paragraph's issue, see the new "fetchlimit" setting in the mailconfig module section ahead; this allows you to limit how many headers PyMailGUI will attempt to fetch, making it practical to use for large inboxes and slow Internet access or mail servers.

Unicode and Internationalization Support

In Version 3.0, there is now support for Unicode (Internationalization) encodings for fetched, saved, and sent mails, as allowed by the Python 3.1 email package. A user-configurable setting in the mailconfig module is used on a session-wide basis to decode full message bytes into Unicode strings when fetched, and to encode and decode mail messages stored in text-mode save files.

More visibly, when composing, the main text and attached text parts of composed mails may be given explicit Unicode encodings in mailconfig or via user input; when viewing, message header information of parsed emails is used to determine the Unicode types of both the main mail text as well as text parts opened on demand. In addition, Internationalized mail headers (e.g., "Subject", "From") are decoded per email, MIME, and Unicode standards when displayed, per their own content, and are automatically encoded if non-ASCII when sent.

Here is how all these policies play out in terms of user interfaces:

The user setting of the mailconfig module that applies to the last of these points is used across an entire PyMailGUI session to decode message bytes to text prior to parsing, and to save and load full message text to save files. Users may set this to a Unicode encoding name string which works for their mails' encodings; 'latin1', 'utf8', and 'ascii' are reasonable guesses for most emails. If this encoding fails, other common encodings are tried, and as a last resort the message is still displayed if its headers can be decoded, but its body is changed to an error message; to view such mails, try running PyMailGUI again with a different encoding.

There is currently no special support for Unicode encodings of the full text of sent mails in general, apart from that inherited from Python's libraries.

The mailconfig Configuration Module

Change the module file in PyMailGUI's home directory on your own machine to reflect your email server names, username, email address, and optional mail signature line added to all composed mails.

Most settings in this module are optional, or have reasonable preset defaults. However, you must minimally set this module's "smtpservername" variable to send mail, and its "popservername" and "popusername" to load mail from a server. These are simple Python variables assigned to strings in this file. See the module file and its embedded comments for details.

The mailconfig module's "listheaders" attribute can also be set to a tuple of string header field name, to customize the set of headers displayed in list windows; mail size is always displayed last. Similarly mailconfig's "viewheaders" attribute can extend the set of headers shown in a View window (though From, To, Cc, and Subject fields are always shown). List windows display message headers in fixed-width columns.

Variables in the mailconfig module also can be used to tailor the font used in list windows ("fontsz"), the column at which viewed and quoted text is automatically wrapped ("wrapsz"), colors and fonts in various windows, the local file where sent messages are saved, the opening of mail parts, and more; see the file's source code for more details.

New in version 3.0: the "fetchEncoding" setting in this file is used across an entire PyMailGUI session to decode message bytes to text prior to parsing, and to save and load full message text to save files. Set this to a Unicode encoding name which works for your mails ('latin1', 'utf8', and 'ascii' are reasonable guesses for most emails). If this encoding along with a few guesses fails, the message will still appear if its headers can be decoded, but its body is changed to an error message; try running again with a different encoding name to view.

New in version 3.0: for sending new mails, "mainTextEncoding" and "attachmentTextEncoding" are used to specify Unicode encodings for main mail text, plus all text attachments. Set these to None to be prompted for encodings on mail sends, otherwise the assignments to these names are used across the entire session (if you "Cancel" when asked, they both default to 'latin-1'). Set these to sys.getdefaultencoding() result to apply the platform default. The system falls back on UTF-8 if your selections do not match text to be sent.

New in version 3.0: "headersEncodeTo" is used to encode non-ASCII headers (and email address names in headers) if it is not None; if None, UTF-8 is the default.

New in version 3.0: PyMailGUI loads only mail headers initially, and only newly arrived headers thereafter. Depending on your Internet and server speeds, though, this may still be impractical for very large inboxes. To support such cases, a new mailconfig setting, "fetchlimit," can be used to limit the number of headers (or full mails if TOP is unsupported) fetched on loads: given this setting N, PyMailGUI fetches at most N of the most recently arrived mails. Older mails outside this set are not fetched from the server, but are displayed as empty/dummy emails which are mostly inpoperative (though they may be fetchable).

New in version 3.0: If "repliesCopyToAll" is True, the Reply operation prefills the reply's Cc line with all original mail recipients, after removing duplicates and the new sender. If it is False, no CC prefill occurs, and the reply is configured to reply to the original sender only. The Cc line may always be edited later in either case.

Note: use caution when changing this file, as PyMailGUI may not run at all if some of its variables are missing. You may wish to make a backup copy before editing it in case you need to restore its defaults. A future version of this system may have a configuration dialog which generates this module's code.

See also: here, for configuring the appearance of pop-up PyEdit windows created by PyMailGUI for test parts, raw mail, and source code (the mailconfig module configures the main text PyEdit component only).


This client-side program currently requires Python and tkinter. It uses Python threads, if installed, to avoid blocking the GUI. Sending and loading email from a server requires an Internet connection. Requires Python 3.0 or later, and uses the Python 3.1 version of the "email" standard library module to parse and compose mail text. Reuses a number of modules located in the PP4E examples tree.

Miscellaneous Hints ("Cheat Sheet")