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

[base60]

MRJ InfoTech Admin wrote:
>>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.

No... they check for the presence of an in-addr, a resolvable domain,
and sending IP being on an RBL.

None require an MX.

> 
> 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.

You're confused.  The in-addr requirement is for the outbound host, and
not the MX associated with the inbound.  The two may be the same, but
many places separate in/outbound email.

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

I would agree that an MX is a good idea, but SPF records tend to create
ancillary issues and most places could care less about them.

> 
> 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.

This doesn't make much sense....

> 
> 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
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