"mail transport unavailable" for few recipients

[goodnight]

Hi. I looking for help.

I use 5.0.18 aboute a year. 3 days ago I found strange problem: some messages (for few recipients) didn't send.

zimbra.log

Apr 26 15:24:40 mail postfix/qmgr[9877]: C21312B68032: to=<user@example.spb.ru>, relay=none, delay=1616, delays=1283/333/0/0, dsn=4.3.0, status=deferred (mail transport unavailable)

Apr 26 16:09:06 mail postfix/qmgr[9877]: 435982B68063: to=<user@example.spb.ru>, relay=none, delay=2687, delays=2686/0.33/0/0, dsn=4.4.1, status=deferred (delivery temporarily suspended: connect to mail2.example.spb.ru[xxx.xxx.xxx.xxx]: Connection timed out)

All messages for this recipients stoping in queue.

Messages for other recipients sending correctly.

Thanks, Sasha