I want to setup a mailserver with a public DNS record. There are already some threads here in the forum, but the most relevant I could find is five years old (Postfix myhostname) and the bug report is closed (https://forge.univention.org/bugzilla/show_bug.cgi?id=30350).
My server admin book is telling me that it is very important, that
postconf myhostname will prompt the DNS registered fdqn. In UCS it is the local DNS fdqn - having the internal domain name in it.
The server setup is actually almost working. The only change I have made to ucr registry is changing the helo name to the public DNS record. This way I can send emails to many email-adresses (including gmail.com, university-servers) - but GMX is telling me:
Feb 16 11:27:54 host postfix/smtp: 9FD80C8252C: to=<firstname.lastname@example.org>, relay=mx01.emig.gmx.net[188.8.131.52]:25, │2018-02-15 23:44:43,651 fail2ban.filter : INFO Set maxRetry = 5 delay=405, delays=404/0.31/0.2/0, dsn=4.0.0, status=deferred (host mx01.emig.gmx.net[184.108.40.206] refused to talk to me: 554-g│2018-02-15 23:44:43,658 fail2ban.filter : INFO Set findtime = 600 mx.net (mxgmx117) Nemesis ESMTP Service not available 554-No SMTP service 554-Bad DNS PTR resource record. 554 For explanation │2018-02-15 23:44:43,659 fail2ban.actions: INFO Set banTime = 600 visit http://postmaster.gmx.com/en/error-messages?ip=my.public.ip.adr&c=rdns)
The solution can of course go in different directions:
- don’t care to change local DNS name in the public sphere
- changing the myhostname setting in main.cf
The question is: what is - for security reasons as well as for system stability - the way I should go? As changing myhostname is not possible through a ucr registry entry. Perhaps telling the world the internal domain-name isn’t a big problem too?
Any thoughts on this are appreciated, kind regards
Edit: the thread poses two questions and a problem (solved) having little to do with the questions - so I will put my questions in a new thread here: Postfix myhostname 4.2