Now, in the evening, when all staff has left the office, I was able to restart the entire Windows Server 2016, not only Mercury. And now Mercury I is working again as expected [:D][:D][:D]. But still have no idea why it failed.

<p>Since today different IMAP clients like Thunderbird and Roundcube are showing "Error 10 Processing FETCH Command" when accessing mailboxes  via Mercury I. With Pmail I still have access to all mailboxes, but with Thunderbird or Roundcube only existing mails (already downloaded in local copy) will be sometimes shown in different folders and new mail folder but they are not able to sync the mails to show new mails. In RoundCube all folders are counting a correct number of read/unread messages but are not able to list/show them all.</p><p>I've also removed a Thunderbird mail account (within TB) and tried to connect completely new. I was able to locate the IMAP server, and could connect to my mail account, but subscribing any existing mail folders was impossible. No folders were available to subscribe. Later I was able to subscribe but syncing all mails let the error appear again and again. BTW, sending mails with TB via MercuryS is still working. </p><p>Mercury has been rebooted already without any chnages. On weekend only a new IERenderer.dll has been copied into Pmail, but shouldn't have any effect to Mercury.</p><p>All IMAP clients are connecting using port 143 without any secure options like SSL since we are connecting from internal LAN only.</p><p>Here Mercury I state window with currently two logged-in users which are unable to sync:</p><p><a mce_href="https://www.dropbox.com/s/9kfk4pnbybiruts/imap.jpg?dl=0" target="_blank" title="Mercury I State" href="https://www.dropbox.com/s/9kfk4pnbybiruts/imap.jpg?dl=0">Mercury I State</a>  </p><p>As follows you can see an extract from an example MI log:</p><p>First a lot of such lines appear in the log for all of my different mail folders:</p><p>11:02:53.340: << * LIST (\NoInferiors) "/" Trash<cr><lf> </p><p>...</p><p>11:02:53.512: << 4 OK LSUB completed.<cr><lf> 11:02:53.528: >> 5 list "" "INBOX"<cr><lf> 11:02:53.528: << * LIST (\NoInferiors) "/" INBOX<cr><lf> 11:02:53.528: << 5 OK LIST completed.<cr><lf> 11:02:53.543: >> 6 list "" "Trash"<cr><lf> 11:02:53.543: << * LIST (\NoInferiors) "/" Trash<cr><lf> 11:02:53.543: << 6 OK LIST completed.<cr><lf> 11:02:53.559: >> 7 create "Trash"<cr><lf> 11:02:53.559: << 7 NO Path or folder creation error (check folder name).<cr><lf> 11:02:53.559: >> 8 select "INBOX"<cr><lf> 11:02:53.575: << * 18 EXISTS<cr><lf> 11:02:53.575: << * 0 RECENT<cr><lf> 11:02:53.575: << * FLAGS (\Deleted \Draft \Seen \Answered)<cr><lf> 11:02:53.575: << * OK [UNSEEN 1] First unread message<cr><lf> 11:02:53.590: << * OK [UIDVALIDITY 1207431611] UID Validity<cr><lf> 11:02:53.590: << * OK [UIDNEXT 5076] Predicted next UID<cr><lf> 11:02:53.590: << * OK [PERMANENTFLAGS (\Deleted \Draft \Seen \Answered)] Settable message flags<cr><lf> 11:02:53.606: << 8 OK [READ-WRITE] SELECT completed.<cr><lf> 11:02:53.606: >> 9 UID fetch 1:* (FLAGS)<cr><lf> 11:02:53.606: << * 1 FETCH (UID 5057 FLAGS () 11:02:53.606: << )<cr><lf> 11:02:53.621: << 9 <b>NO Error 10 processing FETCH command.<cr><lf></b> 11:02:53.621: << 9 OK UID FETCH complete.<cr><lf> 11:03:04.217: >> 10 noop<cr><lf> 11:03:04.232: << 10 OK NOOP complete.<cr><lf> 11:03:04.248: >> 11 logout<cr><lf> 11:03:04.248: << * BYE IMAP4rev1 server terminating connection.<cr><lf> 11:03:04.263: << 11 OK LOGOUT completed.<cr><lf> 11:03:04.263: --- Connection closed at 14 Apr 2020, 11:03:04.263. --- 11:03:04.263:  </p><p>Or another complete log:</p><p>11:03:03.842: --- 14 Apr 2020, 11:03:03.842 --- 11:03:03.842: Accepted connection from '192.168.21.33', port 143, timeout 120 secs. 11:03:03.842: Connection from 192.168.21.33, Tue, 14 Apr 2020 11:03<cr><lf> 11:03:03.857: << * OK <i>domain</i>.com IMAP4rev1 Mercury/32 v4.81.184 server ready.<cr><lf> 11:03:03.857: >> 1 capability<cr><lf> 11:03:03.857: << * CAPABILITY IMAP4rev1 AUTH=PLAIN X-MERCURY-1<cr><lf> 11:03:03.873: << 1 OK CAPABILITY complete.<cr><lf> 11:03:03.873: >> 2 authenticate PLAIN<cr><lf> 11:03:03.873: << +<cr><lf> 11:03:03.888: >> AGptAGouLi4ubQ==<cr><lf> 11:03:03.888: << 2 OK AUTHENTICATE completed.<cr><lf> 11:03:03.888: >> 3 select "2020/Eingang 2020"<cr><lf> 11:03:03.904: << * 364 EXISTS<cr><lf> 11:03:03.904: << * 0 RECENT<cr><lf> 11:03:03.904: << * FLAGS (\Deleted \Draft \Seen \Answered)<cr><lf> 11:03:03.904: << * OK [UIDVALIDITY 1578393783] UID Validity<cr><lf> 11:03:03.920: << * OK [UIDNEXT 396] Predicted next UID<cr><lf> 11:03:03.920: << * OK [PERMANENTFLAGS (\Deleted \Draft \Seen \Answered)] Settable message flags<cr><lf> 11:03:03.920: << 3 OK [READ-WRITE] SELECT completed.<cr><lf> 11:03:03.920: >> 4 UID fetch 1:* (FLAGS)<cr><lf> 11:03:03.935: << * 1 FETCH (UID 1 FLAGS (\Seen) 11:03:03.935: << )<cr><lf> 11:03:03.935: << 4 NO <b>Error 10 processing FETCH command</b>.<cr><lf> 11:03:03.935: << 4 OK UID FETCH complete.<cr><lf> 11:20:30.352: >> 5 close<cr><lf> 11:20:30.367: << 5 OK CLOSE completed.<cr><lf> 11:20:30.367: >> 6 logout<cr><lf> 11:20:30.367: << * BYE IMAP4rev1 server terminating connection.<cr><lf> 11:20:30.367: << 6 OK LOGOUT completed.<cr><lf> 11:20:30.383: --- Connection closed at 14 Apr 2020, 11:20:30.383. --- 11:20:30.383:  </p><p>Has anybody a clue? </p>