On Wed 30 Sep 2026 at 11:40:23 (-0400), Greg Wooledge wrote: > On Wed, Sep 30, 2026 at 10:18:26 -0500, David Wright wrote: > > I don't understand not having any domain name. Surely the hostname > > is a domain name in itself. I ran my network for years like that, > > and exim (as set up by Debian) would moan about the lack of a dot > > in /etc/mailname. > > > > I only added .corp when I found that there was semi-official > > documentation for using that. I chose it in preference to .home > > and .mail merely because grepping -r '\<corp\>' /etc produced > > fewest false positives. Current false positives here are: > > > > home: 173 mail: 162 corp: 0 > > > > I haven't yet bothered to move to .home.arpa. Maybe sometime. > > So, your *system* doesn't have or need a domain name -- only your MTA > needs one.
Disclaimer: I'm no expert on any of this. AIUI, all my hosts are /internal network/ MTAs as they all send their emails to my 24/7 laptop "server". While the domain part might be optional, I have found that it makes reconciling the configuration files with the documentation easier—you can tell the different between hostnames and domains. (It speeds up looking through log files.) I no longer use exim to queue outgoing external emails, as attachments are transferred so quickly that mutt isn't held up for any significant period of time. So my emails like this one get sent directly to a submission port at my email hosting service. I assume mutt (MUA) gets its HELO from /etc/hosts. I don't know whether having only a hostname in the HELO might cause problems with some email providers. Presumably so, in view of: https://lists.debian.org/debian-user/2026/09/msg00467.html > There are two common reasons why people want (or think they want) to > set up a "default domain name": > > 1) To reach other hosts on the network using short names. > > 2) To set up email. > > For case 1, the proper place to set this is in the /etc/resolv.conf > file, which unfortunately in modern ages has been taken over by > software that thinks it knows better than you do, and will overwrite > your /etc/resolv.conf file any time it feels like doing so. > > Steps to work around that are found at <https://wiki.debian.org/resolv.conf>. My resolv.conf files contain only nameserver 192.168.1.1 (the router), and there's no DNS server running there, so DNS queries (except exim) are either resolved by /etc/hosts (internal) or the servers configured in my router (external). None of my 3 routers has a DNS server. I don't know whether some software might erroneously append some domain name when handed just a hostname. If so, then having .corp might prevent this happening, and/or make it obvious to other software that the name is not intended for use on the Internet. > For case 2, an MTA only wants a domain name for two reasons: > > a) So it knows how to introduce itself when it issues a HELO > or EHLO command in SMTP (this is basically saying, "Hello, I am > scooby.davidsdomain.com."). > > b) When you want to send mail to another user within your organization > (e.g. you run something like "echo meeting is at 10:00 | mail stu" > and you expect your MUA/MTA to expand "stu" to "[email protected]"). > > The proper places to set the HELO domain and the default recipient domain > are within the MTA's configuration. Yes, I set .corp when configuring exim, and I can see it end up in /etc/mailname. For exim to find the other hosts on my network, each has a hubbed_hosts file in /etc/exim/ (resembles a hosts file but written domain addr with one name per line rather than sharing addr lines). > Some MTAs cheat a little bit, by trying to derive one or both of > these domain names by looking at your non-mail-specific files, such as > /etc/hosts or /etc/resolv.conf. I wouldn't depend on this. Cheers, David.
