Marc> I had a working container with dovecot configured as proxy. And Marc> all of a sudden I am getting these messages 'dovecot: auth: Marc> Error: DNS lookup for roosit03 failed: Name does not resolve' Marc> Pinging/nslookup these hostnames is ok
Does nslookup work inside the container? Sounds to me like the setup isn't working properly, but it's hard to know unless you give us more details. Can you spin up another container with the same config but not running dovecot to do a check on DNS resolution?
Does the container's logs give you more details? How often do you stop/restart the container? I would think that Dovecot in a container isn't really ideal since you need to access the mailstores, and somehow you get email delivered to the mailstore by postfix/sendmail/exim or some other tool.
John