I don't get mails any longer

On 2014-02-08 I started not getting mails any longer. I have stopped a server before that I thought did not do any mailing functionality.

Symptoms

cat /var/log/mail.err 

delivers

[...]
Feb  8 10:58:00 euve31070 postfix/smtpd[4110]: fatal: no SASL authentication mechanisms
Feb  8 10:58:00 euve31070 postfix/smtpd[4108]: fatal: no SASL authentication mechanisms
Feb  8 10:58:35 euve31070 postfix/smtpd[4119]: fatal: no SASL authentication mechanisms
Feb  8 10:59:36 euve31070 postfix/smtpd[4120]: fatal: no SASL authentication mechanisms
Feb  8 11:00:49 euve31070 postfix/smtpd[4123]: fatal: no SASL authentication mechanisms

I suspect for every incoming mail there is a line.

I cannot send mail via roundcube, it says

SMTP Error (-1): Connection to server failed.

Trying to send mails via thunderbird I get

Sending of message failed.
The message could not be sent because the connection to SMTP server smtp.staerk.de timed out. Try again or contact your network administrator.

telnet smtp.staerk.de 587 is possible however.

It did work on friday. Is a reboot the culprit?

uptime
21:03:02 up 25 days,  5:16,  4 users,  load average: 0.13, 0.07, 0.01

root@euve31070:/etc/postfix# telnet localhost 25
Trying ::1...
Trying 127.0.0.1...
Connected to localhost.
Escape character is '^]'.
EHLO mail.staerk.de
Connection closed by foreign host.