[Dovecot] zlib unexpected EOF

Hi,

I am seeing occasional log entries like:

Feb 4 06:20:01 mail1 dovecot: imap(user@example.com): Error: read(<imap client>) failed: zlib.read(<imap client>): unexpected EOF at 894774 Feb 4 06:20:01 mail1 dovecot: imap(user@example.com): Disconnected in APPEND (1 msgs, 201 secs, 0/5180550 bytes) in=894774 out=643701

I've been able to correlate this to users - using Thunderbird - complaining that they have been unable to "send email".

Is the problem on the Dovecot side, their side or something else?

If on the Dovecot any pointers and what I should look at?

Thanks, Anand