sendmail config help
Jon Radel
jon at radel.com
Tue Jan 5 17:12:49 UTC 2016
On 1/5/16 9:39 AM, Matthew Seaman wrote:
> In fact, even if your mail host uses just the domain as its hostname,
> I'd still have
>
> z.com. IN MX 0 z.com.
>
> Which looks entirely redundant, but the reason to have it is more social
> and reputational rather than technical.
Though if your DNS caching and negative caching times are "normal" I
believe that's also liable to save time if anyone ever sends you more
than one e-mail. In other words, a sending SMTP daemon will [or is
supposed to-YMMV for various spam generating engines] check for an MX
record before it falls back to using the A record directly, and an MX
record is liable to be cached near the sender for longer than the
information that there is no MX record.
Actually, under many circumstances, time will also be saved on the first
e-mail, as the initial query for MX records will frequently trigger a
reply with the appropriate A records included in the additional records
of the response, so the sending daemon won't have to make further
queries for the appropriate A record(s).
Eventually those milliseconds add up. :-)
In other words, unless there is good reason to not have an MX record,
I'd suggest always having an MX record for any name at which you wish to
regularly receive e-mail.
--Jon Radel
jon at radel.com
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