dovecot --version => 2.2.22 (fe789d2)

Scenario:

Sometimes imap client send email correctly but there's is any message stored in sent mail folder

in that scenario I have found an error in my dovecot.log : 

2019-02-11 09:04:52 imap(-----@------------): Info: Disconnected in APPEND (1 msgs, 125 secs, 2818048/4426899 bytes) in=3365352 out=1522206

Question:

what about this?

Is there, in dovecot configuration, a parameter that insist to any kind of APPEND like value.?  I have not find that.

Have you any idea to solve this?

Thanks