After upgrading my mailserver from buster to bullseye and dovecot 2.3.15 to 2.3.17.1 I got the following errors:

Jan 22 14:22:32 Warning: doveadm(user1)<2953060><49b0NRQF7GFkDy0ALVPUUA>: mdbox /local/mail/user1/storage: rebuilding indexes Jan 22 14:22:39 Error: doveadm(user2)<2953112><awsPGB8F7GGYDy0ALVPUUA>: dsync(2nd.dovecot.server): read(compress(/local/mail/user2/storage/m.4650)) failed: read(/local/mail/user2/storage/m.4650) failed: zlib.read(/local/mail/user2/storage/m.4650): unexpected EOF at 7038367 (last sent=mail, last recv=mail_request (EOL))

I have 2 dovecot servers in a multi-master configuration. The both servers are synced with dsync and the users are routed through a dovecot directors.

Any hints where I can continue to investigate / solve this issue?

best regards, arno