doveadm backup has problems with some accounts

I try to setup for our mailserver (in a dc) a job backup to a secondary server (in our office) with "doveadm backup" via the -R option. (rsync , rsnapshot and so on tooks too long at the moment)

For the most user accounts all work as expected, but for three users it always fails

First run: /usr/bin/doveadm -Dv backup -Ru user1 tcp:mua01.domain.intra:12345

Dec 01 08:54:21 doveadm(user1)<70126><qfzHDjyfaWXuEQEAy5X8iQ>: Debug: Mailbox INBOX: Mailbox opened because: copy caching decisions Dec 01 08:54:22 doveadm(user1)<70126><qfzHDjyfaWXuEQEAy5X8iQ>: Warning: Deleting mailbox 'Archiv.Allgemein unsortiert': UID=1 GUID=1350559209.P2052Q54.lin-mail1.intra is missing locally Dec 01 08:54:22 doveadm(user1)<70126><qfzHDjyfaWXuEQEAy5X8iQ>: Debug: brain M: Import Archiv.Allgemein unsortiert: Import change type=save GUID=1350559209.P2052Q54.mail1.intra UID=1 > hdr_hash= result=Reverting local change by deleting mailbox - No more local mails found Dec 01 08:54:22 doveadm(70126): Debug: brain M: Import Archiv.Allgemein unsortiert: Saved UIDs: Dec 01 08:54:22 doveadm(70126): Debug: auth-master: conn unix:/run/dovecot/auth-userdb (pid=661,uid=0): Disconnected: Connection closed (fd=9)

So it aborts on the lines above and a incomplete maildir is on the local server. so the next doveadm try say's that he can't delete INBOX , etc.

Dec 01 09:03:33 doveadm(user1)<70169>: Error: Mailbox INBOX sync: mailbox_delete failed: INBOX can't be deleted.

This a very old account on our server which was migrated over different iterations of our dovecot mailserver. The user behind the account uses outlook over years. Is the space here a problem?

Another user with a similiar issue has the following error message at the end:

Dec 01 09:22:14 doveadm(user2)<70354><RU12FsWlaWXSEgEAy5X8iQ>: Debug: Mailbox INBOX: Mailbox opened because: copy caching decisions Dec 01 09:22:56 doveadm(user2)<70354><RU12FsWlaWXSEgEAy5X8iQ>: Error: read(mua01.domain.intra) failed: EOF (last sent=mailbox, last recv=mailbox) Dec 01 09:22:56 doveadm(70354): Debug: auth-master: conn unix:/run/dovecot/auth-userdb (pid=661,uid=0): Disconnected: Connection closed (fd=9)

I see that the user has a very big inbox? when i check in the source server in the "cur" folder of the INBOX it count's around 269372 mails. Is this perhaps the issue for this message?

And on the last user it looks like:

Dec 01 09:25:19 doveadm(user3)<70376><UoiQAHWmaWXoEgEAy5X8iQ>: Warning: Deleting mailbox 'Entwürfe': UID=1265 GUID=1521832311.M6830P7652.mail-mx1.intra,S=1764,W=1809 is missing locally Dec 01 09:25:19 doveadm(user3)<70376><UoiQAHWmaWXoEgEAy5X8iQ>: Debug: brain M: Import Entwürfe: Import change type=save GUID=1521832311.M6830P7652.mail-mx1.intra,S=1764,W=1809 UID=1265 hdr_hash= result=Reverting local change by deleting mailbox - No more local mails found Dec 01 09:25:19 doveadm(70376): Debug: brain M: Import Entwürfe: Saved UIDs: Dec 01 09:25:19 doveadm(70376): Debug: auth-master: conn unix:/run/dovecot/auth-userdb (pid=661,uid=0): Disconnected: Connection closed (fd=9)

The "Entwürfe" folder directly cannot be the issue? On the filesystem the folder has the name ".Entw&APw-rfe" and also other users has similar folders in their mailboxes.

The source server has dovecot version 2.2.36 (centos 7.9.2009) and the current destination server dovecot version 2.3.16 (ubuntu 22.04 lts)