autoresponse emails not being sent

[michalszypryt]

Hello

I'd like to ask for help in identifying a problem we have with sending out autoresponses.
I am not talking about notifications - those we do not use at all - only about queues>autoresponses so whenever client send us an email he should receive an email with confirmation from us that we did receive it.

I have to say that sending regular emails by our agents to customers works fine but whenever customer sends us email I see that autoresponse record is created but email is not sent out and there are errors in OTRS log:

Fri Sep 7 15:11:06 2018 info OTRS-otrs.PostMasterMailbox.pl-46 Sent auto response (SendAutoReply) for Ticket [2018090746004296] (TicketID=734517, ArticleID=) to 'Client's name <clientemail@gmail.com>'.
Fri Sep 7 15:11:06 2018 error OTRS-otrs.PostMasterMailbox.pl-46 Impossible to send message to: Client's name <clientemail@gmail.com> .
Fri Sep 7 15:11:06 2018 info OTRS-otrs.PostMasterMailbox.pl-46 Error sending message
Fri Sep 7 15:11:06 2018 error OTRS-otrs.PostMasterMailbox.pl-46 Can't send message: 550Start mail input; end with <CRLF>.<CRLF>

We have enabled NET::SMTP but seems that there are no errors in there.

Any help would be appreciated.

BR
Michal

PS I understand that notifications are completely separate thing from autoresponses? Please correct me if I'm wrong here.