Home / server / Questions / 926071
In Process
Vilx-
Asked: 2018-08-13 15:09:16 +0800 CST

In postfix, what's the difference between myhostname and mydomain?

  • 772

I'm trying to set up postfix for the first time. Reading the basic configuration docs, right off the bat I'm faced with two settings that I cannot understand - mydomain and myhostname. I've got the simplest possible situation - a single server for a single domain. Let's call it example.com. My server serves the webpages for http://anything.example.com and I'd like it to receive email for [email protected] as well. (Sending too, but that will be only for authorized users; I'll come to that later)

So, in this case, what's the difference between mydomain and myhostname? Or should they both be simply set to example.com?

Also of note might be that my DNS provider (I don't host it myself) for some reason didn't allow me to put example.com in my MX record. That seemed to be more of a quirk of their system however. I have mail.example.com set there, but *.example.com maps to my IP anyway (in A records), so that shouldn't really matter, right?

domain-name-system

3 Answers

  1. myhostname is the fully qualified domain name. mydomain, is the domain you are using for your email.

    From the docs

    myhostname (default: see "postconf -d" output)

    The internet hostname of this mail system. The default is to use the fully-qualified domain name (FQDN) from gethostname(), or to use the non-FQDN result from gethostname() and append ".$mydomain". $myhostname is used as a default value for many other configuration parameters.

    Example:

    myhostname = host.example.com

    mydomain (default: see "postconf -d" output)

    The internet domain name of this mail system. The default is to use $myhostname minus the first component, or "localdomain" (Postfix 2.3 and later). $mydomain is used as a default value for many other configuration parameters.

    Example:

    mydomain = domain.tld

    • 2

  2. The crucial part of the documentation for both is the following, as it tells us how they are used.

    $myhostname is used as a default value for many other configuration parameters.

    $mydomain is used as a default value for many other configuration parameters.

    To know what you should have in both, consult the output of postconf:

    # postconf -d | grep myhostname
lmtp_lhlo_name = $myhostname
local_transport = local:$myhostname
milter_macro_daemon_name = $myhostname
mydestination = $myhostname, localhost.$mydomain, localhost
myhostname = server.example.com
myorigin = $myhostname
smtp_helo_name = $myhostname
smtpd_banner = $myhostname ESMTP $mail_name
smtpd_proxy_ehlo = $myhostname

    For receiving mail for example.com you only need to have it in mydestination (or virtual_alias_domains etc.) which by default only has $myhostname and localhost.$mydomain. Notice that because mydestination can be configured to include plain example.com (or the variable $mydomain containing it), there's no need to have $myhostname = example.com. The final destination addresses are not directly based on these variables i.e. it doesn't limit the domains you can accept mail for.

    On the other hand, $myhostname is used in smtpd_banner and smtp_helo_name. As RFC 5321, 4.1.1.1 explains, this should be the fully-qualified domain name (FQDN) of the SMTP client (i.e. your server). Some receiving MTAs may validate that the HELO hostname matches the PTR record for the IP address, a mismatch causing additional spam score or in worst case even rejection. Therefore, it's recommended to match $myhostname with whatever there is in the PTR record, and check that the PTR has a corresponding A record.

    Additionally, if you wish to receive mail for [email protected], the *.example.com. A DNS record alone isn't enough (despite it gets used if there's no MX records), but you need to have it listed in your mydestination, too.

    • 2

  3. myhostname is the hostname of the postfix server installed. domain name is the SMTP server domain configured.

    • 0