Bug#994815: exim4: Helo command rejected: need fully-qualified hostname

[Anton Ertl]

On Tue, Sep 21, 2021 at 08:31:15PM +0200, Marc Haber wrote:
> Please check whether your system is correctly configured to find the
> host name. Information can be found on
> https://wiki.debian.org/PkgExim4UserFAQ#How_does_exim_find_out_its_host_name_to_use_in_HELO.2FEHLO.3F
> 
> Please report back about your results.

It's not quite clear to me what you want me to report, but I will try.

We never had a problem of HELO localhost.localdomain, only of HELO
<shortname>.

After commenting out the MAIN_HARDCODE_PRIMARY_HOSTNAME line (and
running update-exim4.conf and service exim4 restart, I got

# exim4 -bP|grep ^primary_hostname
primary_hostname = <shortname>

I then did "apt purge libnss-myhostname" (and again update and
restart) and now the same command produces:

primary_hostname = <longname>

When trying "telnet <hostname> smtp", the mail server identifies itself with
the longname and replies to "helo bla" with

250 <longname> Hello <longname of telnet machine> [<ip>]

So apparently libnss-myhostname bug is at fault.  Looking at bug
report #756224, it has not been fixed in 7 years, so it is unlikely to
be fixed soon, and a conflict between exim4 and libnss-myhostname
seems appropriate.  I don't remember explicitly installing
libnss-myhostname, so it most likely came with some other package;
however, removing it did not lead to other package removals, so I
don't know how it came in.

- anton