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<h2 id="specifications">Specifications</h2> <p>A Maildir <a href="/facts/Directory_(file_systems)/VLtLcEXY">directory</a> (often named Maildir) usually has three subdirectories named tmp, new, and cur.<a class="footnote-ref" id="fnref:2" href="#fn:2"><sup>2</sup></a> </p> <ul><li>The tmp subdirectory temporarily stores e-mail messages that are in the process of being delivered. This subdirectory may also store other kinds of temporary files.</li> <li>The new subdirectory stores messages that have been delivered, but have not yet been seen by any mail application.</li> <li>The cur subdirectory stores messages that have already been seen by mail applications.<a class="footnote-ref" id="fnref:3" href="#fn:3"><sup>3</sup></a></li></ul> <h3>Maildir++</h3> <p>Sam Varshavchik, the author of the <a href="/facts/Courier_Mail_Server/XwCvy7M5">Courier Mail Server</a> and other software, defined the Maildir++ extension<a class="footnote-ref" id="fnref:4" href="#fn:4"><sup>4</sup></a><a class="footnote-ref" id="fnref:5" href="#fn:5"><sup>5</sup></a> to the Maildir format to support subfolders and mail quotas. Maildir++ directories contain subdirectories with names that start with a '.' (dot) which are also Maildir++ folders. The extension complies with the original Maildir specification, which allows for subdirectories in addition to <i>tmp</i>, <i>new</i> and <i>cur</i>. </p> <h2 id="technical-operation">Technical operation</h2> <p>A <a href="/facts/Mail_delivery_agent/Syntl05o">mail delivery agent</a> is a <a href="/facts/Computer_process/Vcq7EnUV">program</a> that delivers an email message into a Maildir. The mail delivery agent creates a new file with a unique filename in the tmp directory.<a class="footnote-ref" id="fnref:6" href="#fn:6"><sup>6</sup></a><a class="footnote-ref" id="fnref:7" href="#fn:7"><sup>7</sup></a><a class="footnote-ref" id="fnref:8" href="#fn:8"><sup>8</sup></a> At the time of its invention guaranteeing unique filenames efficiently was difficult. The original <a href="/facts/Qmail/FeLv8Wyt">qmail</a><a class="footnote-ref" id="fnref:9" href="#fn:9"><sup>9</sup></a> algorithm for unique names was: </p> <ol><li>read the current <a href="/facts/Unix_time/d8Et1sa2">Unix time</a></li> <li>read the current <a href="/facts/Process_identifier/q9TlqHEP">process identifier</a> (PID)</li> <li>read the current <a href="/facts/Hostname/WcLyMFKA">hostname</a></li> <li>concatenate the above three values into a string separated by the <a href="/facts/Full_stop/w0Ylafwn">period character</a>; this is the new filename</li> <li>if <a href="/facts/Stat_(system_call)/5DeWQJFS">stat()</a> reports that the filename exists, then wait two seconds</li> <li>go to previous step until the filename does not exist</li> <li>create a file with the unique filename and write the message contents to the new file</li></ol> <p>By 2000, the qmail author recommended in an updated specification<a class="footnote-ref" id="fnref:10" href="#fn:10"><sup>10</sup></a> to append the value of a per-process counter to the PID, whose value should be incremented after each delivery. The rate-limiting recommendation to "wait two seconds" was dropped. </p><p>By 2003, the recommendations had been further amended to require that instead of the PID and counter, the middle part of the filename should be created by "concatenating enough of the following strings to guarantee uniqueness" even in the face of multiple simultaneous deliveries to the same maildir from one or more processes:<a class="footnote-ref" id="fnref:11" href="#fn:11"><sup>11</sup></a> </p> <ul><li>#<i>n</i>, where <i>n</i> is (in hexadecimal) the output of the operating system's unix_sequencenumber() system call, which returns a number that increases by 1 every time it is called, starting from 0 after reboot.</li> <li>X<i>n</i>, where <i>n</i> is (in hexadecimal) the output of the operating system's unix_bootnumber() system call, which reports the number of times that the system has been booted. Together with #, this guarantees uniqueness; unfortunately, most operating systems don't support unix_sequencenumber() and unix_bootnumber().</li> <li>R<i>n</i>, where <i>n</i> is (in hexadecimal) the output of the operating system's unix_cryptorandomnumber() system call or an equivalent source, such as /dev/urandom. Unfortunately, some operating systems don't include cryptographic random number generators.</li> <li>I<i>n</i>, where <i>n</i> is (in hexadecimal) the UNIX <a href="/facts/Inode/Ej7JIzyP">inode</a> number of this file. Unfortunately, inode numbers aren't always available through <a href="/facts/Network_File_System/jWRRALVo">NFS</a>.</li> <li>V<i>n</i>, where <i>n</i> is (in hexadecimal) the UNIX device number of this file. Unfortunately, device numbers aren't always available through NFS. (Device numbers are also not helpful with the standard UNIX filesystem: a maildir has to be within a single UNIX device for link() and rename() to work.)</li> <li>M<i>n</i>, where <i>n</i> is (in decimal) the microsecond counter from the same gettimeofday() used for the left part of the unique name.</li> <li>P<i>n</i>, where <i>n</i> is (in decimal) the process ID.</li> <li>Q<i>n</i>, where <i>n</i> is (in decimal) the number of deliveries made by this process.</li></ul> <p>This 2003 algorithm was criticised<a class="footnote-ref" id="fnref:12" href="#fn:12"><sup>12</sup></a> in 2006 as being unnecessarily complex by <a href="/facts/Timo_Sirainen/5JCdTNgU">Timo Sirainen</a>, the creator of <a href="/facts/Dovecot_(software)/cNzef2k5">Dovecot</a>. </p><p>As of November 2023, qmail author <a href="/facts/Daniel_J._Bernstein/KQLuMRTx">Daniel Bernstein</a> had made no further changes to the 2003 filename generation recommendations.<a class="footnote-ref" id="fnref:13" href="#fn:13"><sup>13</sup></a> On modern POSIX systems, <a href="/facts/Temporary_file/5PRRodGA">temporary files</a> can be safely created with the <a href="/facts/Mkstemp/yqUkrAqB">mkstemp</a> C library function. </p><p>The delivery process stores the message in the maildir by creating and writing to tmp/<i>uniquefilename</i>, and then moving this file to new/<i>uniquefilename</i>. The moving can be done using <a href="/facts/Rename_(computing)/0FHwfKp2">rename</a>, which is atomic in many systems.<a class="footnote-ref" id="fnref:14" href="#fn:14"><sup>14</sup></a> Alternatively, it can be done by <a href="/facts/Hard_link/Twqdfvlt">hard-linking</a> the file to new and then unlinking the file from tmp. Any leftover file will eventually be deleted. This sequence guarantees that a maildir-reading program will not see a partially written message. There can be multiple programs reading a maildir at the same time. They range from <a href="/facts/Mail_user_agent/pQdW9HtC">mail user agents</a> (MUAs), which access the server's file system directly, through <a href="/facts/Internet_Message_Access_Protocol/QMnyvUwk">Internet Message Access Protocol</a> or <a href="/facts/Post_Office_Protocol/QCp6qJQm">Post Office Protocol</a> servers acting on behalf of remote MUAs, to utilities such as <a href="/facts/Biff_(Unix)/X050HfA6">biff</a> and <a href="/facts/Rsync/H4UlsQ3U">rsync</a>, which may or may not be aware of the maildir structure. Readers should never look in tmp. </p><p>When a cognizant maildir-reading process (either a <a href="/facts/Post_Office_Protocol/QCp6qJQm">POP</a> or <a href="/facts/Internet_Message_Access_Protocol/QMnyvUwk">IMAP</a> server, or a mail user agent acting locally) finds messages in the new directory, it <i>must</i> move them to cur. It is just a means to notify the user "you have <i>X</i> new messages".<a class="footnote-ref" id="fnref:15" href="#fn:15"><sup>15</sup></a> This moving needs to be done using the atomic filesystem rename(), as the alternative <i>link-then-unlink</i> technique is non-atomic and may result in duplicated messages. An informational suffix is appended to filenames at this stage. It consists of a <a href="/facts/Colon_(punctuation)/se9fjJa4">colon</a> (to separate the unique part of the filename from the actual information), a "2", a <a href="/facts/Comma/mcW9dcGT">comma</a> and various <a href="/facts/Flag_(computing)/fWgTjqvX">flags</a>. The "2" specifies the version of the information that follows the comma. "2" is the only currently officially specified version, "1" being an experimental version. The specification defines flags that show whether the message has been read, deleted and so on: the initial (capital) letter of "Passed", "Replied", "Seen", "Trashed", "Draft", and "Flagged".<a class="footnote-ref" id="fnref:16" href="#fn:16"><sup>16</sup></a> Applications often choose to supplement this very limited set of flags, for example notmuch<a class="footnote-ref" id="fnref:17" href="#fn:17"><sup>17</sup></a> offers flag synchronization in addition to arbitrary user-defined flags,<a class="footnote-ref" id="fnref:18" href="#fn:18"><sup>18</sup></a> while Dovecot uses lowercase letters to match 26 IMAP keywords,<a class="footnote-ref" id="fnref:19" href="#fn:19"><sup>19</sup></a> which may include keywords such as $<a href="/facts/Message_Disposition_Notification/kqBXDVKs">MDNSent</a> or user-defined flags. </p><p>Although Maildir was intended to allow lockless usage, in practice some software that uses Maildirs also uses locks, such as Dovecot.<a class="footnote-ref" id="fnref:20" href="#fn:20"><sup>20</sup></a> </p> <h2 id="file-system-compatibility-issues">File-system compatibility issues</h2> <p>The Maildir standard can only be implemented on systems that accept colons in filenames. <a class="footnote-ref" id="fnref:21" href="#fn:21"><sup>21</sup></a> </p><p>Systems that don't allow colons in filenames (this includes <a href="/facts/Microsoft_Windows/bwhAhuSL">Microsoft Windows</a> and some configurations of <a href="/facts/Novell_Storage_Services/69Ix126V">Novell Storage Services</a>) can use a non-standard alternative separator, such as ";" or "-". It is often trivial to patch <a href="/facts/Free_and_open-source_software/1cHtjLCB">free and open-source software</a> to use a different separator.<a class="footnote-ref" id="fnref:22" href="#fn:22"><sup>22</sup></a> </p><p>As there is currently no agreement on what character this alternative separator should be, there can be interoperability difficulties between different Maildir-supporting programs on these systems. However, not all Maildir-related software needs to know what the separator character is, because not all Maildir-related software needs to be able to read or modify the flags of a message ("read", "replied to" etc.); software that merely delivers to a Maildir or archives old messages from it based only on date, should work no matter what separator is in use. If only the <a href="/facts/Email_client/pQdW9HtC">MUA</a> needs to read or modify message flags, and only one MUA is used, then non-standard alternative separators may be used without interoperability problems. </p> <h2 id="software-that-supports-maildir-directly">Software that supports Maildir directly</h2> <h3><a href="/facts/Mail_Transfer_Agent/9SJG5sbb">Mail servers</a></h3> <ul><li><a href="/facts/Dovecot_(software)/cNzef2k5">Dovecot</a> IMAP server</li> <li><a href="/facts/Courier_Mail_Server/XwCvy7M5">Courier Mail Server</a> SMTP and IMAP server, for which the Maildir++ format was invented</li> <li><a href="/facts/Sendmail/NBXSd1JA">Sendmail</a> The original SMTP server</li> <li><a href="/facts/Exim/CRVTpcoY">Exim</a> SMTP server</li> <li><a href="/facts/Postfix_(software)/W7X3cFN8">Postfix</a> SMTP server</li> <li><a href="/facts/Qmail/FeLv8Wyt">qmail</a> SMTP server, for which the Maildir format was invented</li> <li><a href="/facts/MeTA1/we6kXEqR">MeTA1</a> SMTP server</li> <li><a href="/facts/OpenSMTPD/9FVzQMuc">OpenSMTPD</a> SMTP server</li> <li><a href="https://stalw.art/">Stalwart Mail Server</a>, SMTP and IMAP server implemented in <a href="/facts/Rust_(programming_language)/8JNMV19F">Rust</a></li></ul> <h3><a href="/facts/Mail_delivery_agent/Syntl05o">Delivery agents</a></h3> <ul><li><a href="/facts/Procmail/88LdCU1q">procmail</a></li> <li><a href="/facts/Dovecot_(software)/cNzef2k5">Dovecot</a> delivery agent</li> <li><a href="/facts/Maildrop/cMxHMmgX">maildrop</a></li> <li><a href="/facts/Getmail/TfCNze09">getmail</a>, a Maildir-aware mail-retrieval and delivery agent alternative to <a href="/facts/Fetchmail/g0sraILY">Fetchmail</a></li> <li><a href="/facts/Fdm_(software)/5oVse8PF">fdm</a></li> <li><a href="https://www.muchsync.org/">muchsync</a>, synchronising <a href="https://notmuchmail.org">notmuch mail</a> mailboxes between any number of replicas</li> <li><a href="/facts/OfflineIMAP/mcvLB37p">OfflineIMAP</a></li> <li><a href="https://isync.sourceforge.io/">isync</a>, synchronises mailboxes, supporting Maildir and IMAP4</li> <li><a href="https://github.com/phlummox/attomail">Attomail</a>, a minimal Maildir-aware MDA implemented in Haskell</li></ul> <h3><a href="/facts/Mail_user_agent/pQdW9HtC">Mail readers</a></h3> <ul><li>aerc<a class="footnote-ref" id="fnref:23" href="#fn:23"><sup>23</sup></a> (efficient and extensible email client)</li> <li><a href="/facts/Balsa_(e-mail_client)/6yoX1LIE">Balsa</a> previously the official GNOME mail reader (prior to Evolution)</li> <li>Cone a curses-based mail reader</li> <li><a href="/facts/Evolution_(software)/4dr857Mg">Evolution</a>, official GNOME mail client</li> <li><a href="/facts/GNUMail/W9ly4oed">GNUMail</a></li> <li><a href="/facts/Gnus/uNM2pErW">Gnus</a></li> <li><a href="/facts/KMail/UHTSTsbl">KMail</a>, KDE mail reader</li> <li><a href="/facts/Mailx/QMmV2M2J">mailx</a></li> <li><a href="/facts/Mutt_(email_client)/touyN3AY">Mutt</a></li> <li>Notmuch<a class="footnote-ref" id="fnref:24" href="#fn:24"><sup>24</sup></a> (fast, global-search and tag-based email system)</li> <li><a href="/facts/Alpine_(email_client)/uxkwJc0u">Pine/Alpine</a></li> <li><a href="/facts/Mozilla_Thunderbird/20lnTsYS">Mozilla Thunderbird</a> – experimental and “disabled by default because there are still many bugs” <a class="footnote-ref" id="fnref:25" href="#fn:25"><sup>25</sup></a></li></ul> <h2 id="notes-and-references">Notes and references</h2> <h2 id="see-also">See also</h2> <ul><li><a href="/facts/Mbox/r6eBSz0L">mbox</a></li> <li><a href="/facts/MH_Message_Handling_System/f4CBduT8">MH Message Handling System</a></li> <li><a href="/facts/MIX_(email)/k747Ivos">MIX (email)</a></li></ul> <h2 id="external-links">External links</h2> <ul><li><a href="https://manpages.debian.org/stretch/qmail/maildir.5.en.html">manual page for maildir</a></li> <li><a href="http://cr.yp.to/proto/maildir.html">maildir specifications</a></li></ul> <h2 id="references">References</h2> <ol> <li id="fn:1"><p>Bernstein, Daniel J. (1995). "maildir(5)". Archived from the original on 1997-10-12. Retrieved 2018-11-23. <a href="/wiki/Daniel_J._Bernstein" target="_blank">/wiki/Daniel_J._Bernstein</a> <a href="#fnref:1" class="footnote-back-ref">↩</a></p></li> <li id="fn:2"><p>Blum, Richard (2001). Postfix. Sams Publishing. ISBN 978-0-672-32114-6. <a href="978-0-672-32114-6" target="_blank">978-0-672-32114-6</a> <a href="#fnref:2" class="footnote-back-ref">↩</a></p></li> <li id="fn:3"><p>Varshavchik, Sam (2009). "maildir(5)". Archived from the original on 2024-04-17. Retrieved 2024-08-09. <a href="http://www.courier-mta.org/maildir.html" target="_blank">http://www.courier-mta.org/maildir.html</a> <a href="#fnref:3" class="footnote-back-ref">↩</a></p></li> <li id="fn:4"><p>Varshavchik, Sam (2009). "maildir(5)". Archived from the original on 2024-04-17. Retrieved 2024-08-09. <a href="http://www.courier-mta.org/maildir.html" target="_blank">http://www.courier-mta.org/maildir.html</a> <a href="#fnref:4" class="footnote-back-ref">↩</a></p></li> <li id="fn:5"><p>Varshavchik, Sam (2011). "Maildir++". Archived from the original on 2024-05-29. Retrieved 2024-08-09. <a href="http://www.courier-mta.org/imap/README.maildirquota.html" target="_blank">http://www.courier-mta.org/imap/README.maildirquota.html</a> <a href="#fnref:5" class="footnote-back-ref">↩</a></p></li> <li id="fn:6"><p>Bernstein., Daniel J. (c. 2000) [First published 2000 or earlier]. "Using maildir format". Archived from the original on 2000-09-02. Retrieved 2018-11-23. <a href="/wiki/Daniel_J._Bernstein" target="_blank">/wiki/Daniel_J._Bernstein</a> <a href="#fnref:6" class="footnote-back-ref">↩</a></p></li> <li id="fn:7"><p>Dovecot Wiki: maildir format <a href="https://doc.dovecot.org/admin_manual/mailbox_formats/maildir/" target="_blank">https://doc.dovecot.org/admin_manual/mailbox_formats/maildir/</a> <a href="#fnref:7" class="footnote-back-ref">↩</a></p></li> <li id="fn:8"><p>Varshavchik, Sam (2009). "maildir(5)". Archived from the original on 2024-04-17. Retrieved 2024-08-09. <a href="http://www.courier-mta.org/maildir.html" target="_blank">http://www.courier-mta.org/maildir.html</a> <a href="#fnref:8" class="footnote-back-ref">↩</a></p></li> <li id="fn:9"><p>Bernstein, Daniel J. (1995). "maildir(5)". Archived from the original on 1997-10-12. Retrieved 2018-11-23. <a href="/wiki/Daniel_J._Bernstein" target="_blank">/wiki/Daniel_J._Bernstein</a> <a href="#fnref:9" class="footnote-back-ref">↩</a></p></li> <li id="fn:10"><p>Bernstein., Daniel J. (c. 2000) [First published 2000 or earlier]. "Using maildir format". Archived from the original on 2000-09-02. Retrieved 2018-11-23. <a href="/wiki/Daniel_J._Bernstein" target="_blank">/wiki/Daniel_J._Bernstein</a> <a href="#fnref:10" class="footnote-back-ref">↩</a></p></li> <li id="fn:11"><p>Bernstein., Daniel J. (2003) [The earliest version of this document was first published in 2000 or earlier]. "Using maildir format". Archived from the original on 2003-04-01. Retrieved 2018-11-23. <a href="/wiki/Daniel_J._Bernstein" target="_blank">/wiki/Daniel_J._Bernstein</a> <a href="#fnref:11" class="footnote-back-ref">↩</a></p></li> <li id="fn:12"><p>Sirainen, Timo. "Maildir Mailbox Format: Mail Delivery'". Archived from the original on 2024-06-24. Retrieved 2024-08-09. All this trouble is rather pointless. Only the first step is what really guarantees that the mails won't get overwritten, the rest just sounds nice. Even though they might catch a problem once in a while, they give no guaranteed protection and will just as easily pass duplicate filenames through and overwrite existing mails.¶ Step 2 is pointless because there's a race condition between steps 2 and 3. PID/host combination by itself should already guarantee that it never finds such a file. If it does, something's broken and the stat() check won't help since another process might be doing the same thing at the same time, and you end up writing to the same file in tmp/, causing the mail to get corrupted.¶ In step 4 the link() would fail if an identical file already existed in the Maildir, right? Wrong. The file may already have been moved to cur/ directory, and since it may contain any number of flags by then you can't check with a simple stat() anymore if it exists or not.¶ Step 2 was pointed out to be useful if clock had moved backwards. However, this doesn't give any actual safety guarantees because an identical base filename could already exist in cur/. Besides if the system was just rebooted, the file in tmp/ could probably be even overwritten safely (assuming it wasn't already link()ed to new/).¶ So really, all that's important in not getting mails overwritten in your Maildir is step 1: Always create filenames that are guaranteed to be unique. Forget about the 2 second waits and such that the Qmail's man page talks about. <a href="/wiki/Timo_Sirainen" target="_blank">/wiki/Timo_Sirainen</a> <a href="#fnref:12" class="footnote-back-ref">↩</a></p></li> <li id="fn:13"><p>"Wayback Machine snapshots of cr.yp.to/proto/maildir.html". Internet Archive. 2023. Retrieved 2023-11-23. <a href="https://web.archive.org/web/20230503185934/cr.yp.to/proto/maildir.html" target="_blank">https://web.archive.org/web/20230503185934/cr.yp.to/proto/maildir.html</a> <a href="#fnref:13" class="footnote-back-ref">↩</a></p></li> <li id="fn:14"><p>"rename". The Open Group. 2013. Retrieved 23 July 2016. That specification requires that the action of the function be atomic. <a href="http://pubs.opengroup.org/onlinepubs/9699919799/functions/rename.html" target="_blank">http://pubs.opengroup.org/onlinepubs/9699919799/functions/rename.html</a> <a href="#fnref:14" class="footnote-back-ref">↩</a></p></li> <li id="fn:15"><p>Sam Varshavchik (25 July 2016). "Management of maildir structures". courier-users (Mailing list). Retrieved 26 July 2016. <a href="http://www.mail-archive.com/courier-users@lists.sourceforge.net/msg38512.html" target="_blank">http://www.mail-archive.com/courier-users@lists.sourceforge.net/msg38512.html</a> <a href="#fnref:15" class="footnote-back-ref">↩</a></p></li> <li id="fn:16"><p>Bernstein., Daniel J. (2003) [The earliest version of this document was first published in 2000 or earlier]. "Using maildir format". Archived from the original on 2003-04-01. Retrieved 2018-11-23. <a href="/wiki/Daniel_J._Bernstein" target="_blank">/wiki/Daniel_J._Bernstein</a> <a href="#fnref:16" class="footnote-back-ref">↩</a></p></li> <li id="fn:17"><p>"Notmuch mail system homepage". notmuchmail.org. Retrieved 2019-06-22. <a href="https://notmuchmail.org/" target="_blank">https://notmuchmail.org/</a> <a href="#fnref:17" class="footnote-back-ref">↩</a></p></li> <li id="fn:18"><p>"notmuch 0.38.3 documentation". notmuch-config. Retrieved 2024-04-17. <a href="https://notmuchmail.org/doc/latest/man1/notmuch-config.html#nmconfig-maildir.synchronize_flags" target="_blank">https://notmuchmail.org/doc/latest/man1/notmuch-config.html#nmconfig-maildir.synchronize_flags</a> <a href="#fnref:18" class="footnote-back-ref">↩</a></p></li> <li id="fn:19"><p>Dovecot Wiki: maildir format <a href="https://doc.dovecot.org/admin_manual/mailbox_formats/maildir/" target="_blank">https://doc.dovecot.org/admin_manual/mailbox_formats/maildir/</a> <a href="#fnref:19" class="footnote-back-ref">↩</a></p></li> <li id="fn:20"><p>Sirainen, Timo. "Maildir Mailbox Format: Locking". Archived from the original on 2024-06-24. Retrieved 2024-08-09. <a href="/wiki/Timo_Sirainen" target="_blank">/wiki/Timo_Sirainen</a> <a href="#fnref:20" class="footnote-back-ref">↩</a></p></li> <li id="fn:21"><p>"mailbox — Manipulate mailboxes in various formats". Python documentation. Retrieved 2023-06-19. <a href="https://docs.python.org/3/library/mailbox.html" target="_blank">https://docs.python.org/3/library/mailbox.html</a> <a href="#fnref:21" class="footnote-back-ref">↩</a></p></li> <li id="fn:22"><p>mutt maildir support: workaround for filesystems that don't accept colons <a href="https://marc.info/?l=mutt-users&m=131644437917477&w=2" target="_blank">https://marc.info/?l=mutt-users&m=131644437917477&w=2</a> <a href="#fnref:22" class="footnote-back-ref">↩</a></p></li> <li id="fn:23"><p>"aerc - the world's best email client homepage". aerc-mail.org. <a href="https://aerc-mail.org/" target="_blank">https://aerc-mail.org/</a> <a href="#fnref:23" class="footnote-back-ref">↩</a></p></li> <li id="fn:24"><p>"Notmuch mail system homepage". notmuchmail.org. Retrieved 2019-06-22. <a href="https://notmuchmail.org/" target="_blank">https://notmuchmail.org/</a> <a href="#fnref:24" class="footnote-back-ref">↩</a></p></li> <li id="fn:25"><p>"Maildir in Thunderbird". mozilla.org. Retrieved 2020-12-06. <a href="https://support.mozilla.org/en-US/kb/maildir-thunderbird" target="_blank">https://support.mozilla.org/en-US/kb/maildir-thunderbird</a> <a href="#fnref:25" class="footnote-back-ref">↩</a></p></li> </ol>