Do I really need an MX record? (for e-mail to work)

[MRJ InfoTech Admin]

>
>It's generally recommended to have MX records.  I've heard anecdotal
>tales of SMTP implementations that don't properly fall back to A
>records, although I don't really have much sympathy for them.  There's
>also a small DNS performance benefit, as it means only one lookup (MX)
>rather than two (MX followed by A).
>
> > ps:  There seems to be no SMTP-specific newsgroup for talking about the
> > benefits and pitfalls of not having an MX record (and no, NANAE does
> > not seem relavent).  Are there any web forums for SMTP discussions?
>
>There's a comp.mail.* hierarchy.
>
>--
>Barry Margolin, barmar at alum.mit.edu


The problems you will likely see is impossible transfer of mail to 
hotmail.com, yahoo.com and gmail.com servers.

In my experience, though limited with non Windows installs, your mail 
server will have a performance issue in the end,
trying to relay a message to these three domains but being unable to do so 
for the sole purpose that they don't recognize
the reverse lookup or are unable to do one of your server/s.

Having an MX and SPF record in place in the zone file will avoid any such 
issues.

The alternative, since you seem happy not to receive spam, is to inform 
your mail server users not to send
to the specified domains, however, it is nearly impossible to tell all your 
customers not to send from these domains.

So way it carefully, the benefit of not getting spam, and the option of not 
getting potential customers emails at all.

If you keep it as is, also verify the functionality of your mail servers 
handling of retry when sending invalidated emails.
You may end up stockpiling messages in the out que.

MRJ