https://build.opensuse.org/package/view_file/server:mail/postfix/postfix-main.cf.patch?expand=1

    myhostname = localhost

If you have more than one postfix (server -> mta -> inet), the email will
bounce at first hop.

Upstream myhostname default is nothing (resulting in gethostname()).
Even the sysconfig will do "$(hostname -f)" if blank.

For those of us not using sysconfig, the default setting of localhost is no
sane. Please remove the line for the safe default or leave it blank.


The example error if both servers are set to localhost:

mailrelay1 postfix/smtp[7779]: warning: host webmail.dev02.net[10.122.2.172]:25
greeted me with my own hostname localhost
mailrelay1 postfix/smtp[7779]: warning: host webmail.dev02.net[10.122.2.172]:25
replied to HELO/EHLO with my own hostname localhost
6C01F1C015E8: to=<test@test.uk>, relay=webmail.dev02.net[10.122.2.172]:25,
delay=0.01, delays=0.01/0/0/0, dsn=5.4.6, status=bounced (mail for
[webmail.dev02.net]:25 loops back to myself)