Thanks for reply,
mail.err is empty and syslog other than a bunch of samba errors contains this from thunderbird which is ok.
Jul 25 15:32:32 zenserver dovecot: imap-login: Login: user=<
xxx@yyy.com>, method=PLAIN, rip=10.10.1.3, lip=10.10.1.38, mpid=3759, TLS, session=<CbzdDaLk29IKCgED>
and in syslog same error as mail log from my client.
Jul 25 15:36:34 zenserver postfix/smtpd[3996]: connect from paulwin7.youdo.local[10.10.1.3]
Jul 25 15:36:34 zenserver postfix/smtpd[3996]: lost connection after CONNECT from paulwin7.youdo.local[10.10.1.3]
Jul 25 15:36:34 zenserver postfix/smtpd[3996]: disconnect from paulwin7.youdo.local[10.10.1.3] commands=0/0
Jul 25 15:36:35 zenserver dovecot: imap-login: Disconnected (no auth attempts in 0 secs): user=<>, rip=10.10.1.3, lip=10.10.1.38, session=<YqZaHKLkzNUKCgED>
and when thunderbird send mail from mailog.
Jul 25 15:41:06 zenserver postfix/smtp[4104]: D818222300D: to=<
aaa@gmail.com>, relay=gmail-smtp-in.l.google.com[108.177.15.26]:25, delay=0.71, delays=0.08/0.01/0.26/0.36, dsn=2.0.0, status=sent (250 2.0.0 OK 1658760066 c7-20020a056000184700b0021d2cec6428si1677924wri.10 - gsmtp)
Jul 25 15:41:06 zenserver postfix/qmgr[2741]: D818222300D: removed
Jul 25 15:41:13 zenserver dovecot: imap-login: Login: user=<
xxx@yyy.com>, method=PLAIN, rip=10.10.1.3, lip=10.10.1.38, mpid=4130, TLS, session=<nYv3LKLke9gKCgED>