Look Up MX Records with /mx

The /mx rule-testing command causes sendmail to look up a specified hostname and return a list of MX records for that host. The form for this command looks like this:

/mx host

Here, host is the short or fully qualified name of a host. If host is missing, sendmail prints the following usage message:

Usage: /mx address

When host exists and has MX records associated with it, sendmail will look up and print those records. The MX records are listed in the order in which they will be tried (lowest to highest preference values). For example:

> /mx ourhost
getmxrr(ourhost) returns 2 value(s):
        mx.our.domain
        offsite.mx.domain
>

If no MX records are found (as for a.com), sendmail prints the following message:

getmxrr(a.com) returns 0 value(s):

When multiple MX records have the same preference values, sendmail randomizes the list. During a single run of sendmail, the randomization will be the same each time. You can see this by looking up aol.com:

> /mx aol.com
getmxrr(aol.com) returns 4 value(s):
        mailin-02.mx.aol.com.
        mailin-01.mx.aol.com.
        mailin-04.mx.aol.com.
        mailin-03.mx.aol.com.

If you have defined the FallbackMXhost option (FallbackMXhost on page 1030) the host that is specified in that option will always appear last in the list of MX hosts. As a side benefit, the fallback host will also be listed for hosts that do not exist:

% /usr/sbin/sendmail -OFallBackMXhost=mx.our.domain -bt
ADDRESS TEST MODE (ruleset 3 NOT automatically invoked)
Enter <ruleset> <address>
> /mx ...

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