Hello,
With my configuration Dovecot creates multiple duplicates (sometimes 2, sometimes 3, sometimes a plenty) of mailfiles when moving them into the Sent or the Trash folders. This does not affect the Inbox folder. I observed this while using Thunderbird on Ubuntu as a client as well as K9-Mail on Android, therefore I expect this comes from the Dovecot server and not from the client itself. It also appears that the duplicates does not have the size S= and vsize W= flags.
Here is a short example of the last emails from my folder /.Sent/cur:
-rw------- 1 pi pi 1,6M mars 24 22:18 1585084691.M834293P16489.raspberry-pi,S=1658182,W=1679758:2,S -rwx------ 1 pi pi 34M mars 24 22:20 1585084841.M415421P17104Q0Rc311b18de2edf536.raspberry-pi:2, -rwx------ 1 pi pi 34M mars 24 22:22 1585084954.M254398P17175Q0R6c5a66e22ac3a3d2.raspberry-pi:2, -rwx------ 1 pi pi 34M mars 24 22:46 1585086411.M317404P18117Q0R61ba34fb281e8eb5.raspberry-pi:2, -rwx------ 1 pi pi 34M mars 24 22:51 1585086659.M435086P18251Q0R7e118d3bd7784c6d.raspberry-pi:2, -rwx------ 1 pi pi 34M mars 24 22:53 1585086799.M821376P18319Q0R6b838db7f14a2302.raspberry-pi:2, -rwx------ 1 pi pi 34M mars 24 22:54 1585086861.M788796P18398Q0Raaa98233db1f9b6a.raspberry-pi:2, -rwx------ 1 pi pi 34M mars 24 23:00 1585087244.M616219P18629Q0R4d5856ac0d1b1337.raspberry-pi:2, -rwx------ 1 pi pi 34M mars 24 23:01 1585087278.M581756P18651Q0R6a75f871d9e8f0aa.raspberry-pi:2, -rwx------ 1 pi pi 34M mars 24 23:01 1585087296.M954701P18666Q0R0cce469807cb0aa8.raspberry-pi:2, -rwx------ 1 pi pi 34M mars 24 23:05 1585087552.M557221P18793Q0R541dece72da12039.raspberry-pi:2, -rwx------ 1 pi pi 34M mars 24 23:09 1585087759.M768686P18927Q0Rbc1c813e1b124702.raspberry-pi:2, -rwx------ 1 pi pi 34M mars 24 23:10 1585087823.M232119P19026Q0R4086d52491835470.raspberry-pi:2, -rwx------ 1 pi pi 34M mars 24 23:10 1585087855.M951407P19035Q0R4edd76369b804f54.raspberry-pi:2, -rwx------ 1 pi pi 34M mars 24 23:22 1585088561.M364587P19476Q0Rdc0ac3a664f1a80f.raspberry-pi:2, -rwx------ 1 pi pi 34M mars 24 23:24 1585088639.M90555P19512Q0R6214b0e915c88908.raspberry-pi:2, -rwx------ 1 pi pi 34M mars 24 23:27 1585088859.M192671P19663Q0Re4562fb440f7a4be.raspberry-pi:2, -rwx------ 1 pi pi 34M mars 24 23:28 1585088927.M926251P19699Q0Rbe7523140efc06e2.raspberry-pi:2, -rwx------ 1 pi pi 34M mars 24 23:29 1585088962.M120826P19721Q0Rd66b5d585c41123b.raspberry-pi:2, -rwx------ 1 pi pi 34M mars 24 23:31 1585089111.M427988P19799Q0R5b8e8a032adc33c8.raspberry-pi:2, -rwx------ 1 pi pi 1,6M mars 24 23:32 1585089138.M910049P19827Q1R1b4d834fadfb0fd6.raspberry-pi:2, -rwx------ 1 pi pi 34M mars 24 23:33 1585089180.M811880P19839Q0R8c415b8fbf638018.raspberry-pi:2, -rwx------ 1 pi pi 34M mars 24 23:34 1585089252.M333476P19878Q0R3b809c0f458a90e0.raspberry-pi:2, -rwx------ 1 pi pi 34M mars 24 23:34 1585089293.M103544P19918Q0Rd9acc8d53f5c8b32.raspberry-pi:2, -rwx------ 1 pi pi 34M mars 24 23:35 1585089314.M270143P19948Q0R1202a6fe81862880.raspberry-pi:2, -rw------- 1 pi pi 2,0M mars 29 13:01 1585479708.M437415P11486.raspberry-pi,S=2076767,W=2105374:2,S -rwx------ 1 pi pi 2,0M mars 29 13:02 1585479733.M94224P13150Q0R974361f29d7d9cdb.raspberry-pi:2, -rw------- 1 pi pi 2,5K mars 31 09:10 1585638623.M921769P12803.raspberry-pi,S=2511,W=2585:2,S -rwx------ 1 pi pi 3,0K mars 31 09:11 1585638671.M552885P12861Q0R878fb6aa8485b5c0.raspberry-pi:2, -rw------- 1 pi pi 19M avril 3 09:38 1585899475.M669440P24679.raspberry-pi,S=19757959,W=20028662:2,S -rwx------ 1 pi pi 19M avril 3 09:38 1585899531.M744009P25082Q0R0b61c7e8e7b723b4.raspberry-pi:2, -rw------- 1 pi pi 421 avril 3 14:52 1585918350.M591326P1027.raspberry-pi,S=421,W=434:2,S -rw------- 1 pi pi 421 avril 3 14:52 1585918360.M206900P1027.raspberry-pi,S=421,W=434:2,S -rw------- 1 pi pi 421 avril 3 14:52 1585918372.M255849P1032.raspberry-pi,S=421,W=434:2,S -rwx------ 1 pi pi 1,1K avril 3 14:53 1585918394.M224204P1071Q0R7e9bc28b2d8e7fc4.raspberry-pi:2, -rwx------ 1 pi pi 1,1K avril 3 14:53 1585918395.M884727P1073Q1Ra4a111c1e0f5a399.raspberry-pi:2, -rwx------ 1 pi pi 1,1K avril 3 14:53 1585918398.M36019P1077Q2R10960cdc588b3ede.raspberry-pi:2,
Below are details about my configuration
pi@raspberry-pi:~$ sudo uname --all Linux raspberry-pi 4.4.38+ #938 Thu Dec 15 15:17:54 GMT 2016 armv6l GNU/Linux
pi@raspberry-pi:~$ mount [...] /dev/sda1 on /home/pi type ext4 (rw,noatime,nodiratime,data=ordered) [...]
pi@raspberry-pi:/var/log$ sudo dovecot --version 2.2.13
pi@raspberry-pi:/var/log$ sudo dovecot -n # 2.2.13: /etc/dovecot/dovecot.conf # OS: Linux 4.4.38+ armv6l Debian 8.0 ext4 disable_plaintext_auth = no mail_location = maildir:/home/pi/Mails/%u namespace { inbox = yes location = mailbox { auto = subscribe special_use = \Drafts name = Drafts } mailbox { special_use = \Junk name = Junk } mailbox { auto = subscribe special_use = \Sent name = Sent } mailbox { special_use = \Sent name = Sent Messages } mailbox { auto = subscribe special_use = \Trash name = Trash } prefix = separator = / type = private name = inbox } passdb { driver = pam } passdb { args = /home/pi/Mails/dovecot_passwords driver = passwd-file } protocols = " imap" service replication-notify-fifo { name = aggregator } service anvil-auth-penalty { name = anvil } service auth-worker { name = auth-worker } service auth-client { name = auth } service config { name = config } service dict { name = dict } service login/proxy-notify { name = director } service dns-client { name = dns_client } service doveadm-server { name = doveadm } service { inet_listener { address = * port = 4143 name = imap } name = imap-login } service imap-urlauth { name = imap-urlauth-login } service imap-urlauth-worker { name = imap-urlauth-worker } service token-login/imap-urlauth { name = imap-urlauth } service login/imap { name = imap } service indexer-worker { name = indexer-worker } service indexer { name = indexer } service ipc { name = ipc } service lmtp { name = lmtp } service log-errors { name = log } service pop3 { name = pop3-login } service login/pop3 { name = pop3 } service replicator-doveadm { name = replicator } service login/ssl-params { name = ssl-params } service stats-mail { name = stats } ssl_cert =