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

[base60]

Peter Dambier wrote:
> sm5w2 at hotmail.com wrote:
> 
>>Because of a recent change to our internet connection, I discovered
>>that our MX record has been essentially non-existant for the past 2 or
>>3 weeks.  Our A record is fine.
>>
>>It's easy enough to configure our MX record, but I'm reluctant to do so
>>because:
>>
>>1) We are getting e-mail, and there is no indication that anyone trying
>>to send us e-mail is encountering any difficulty
> 
> 
> I remember originally I sent and received email using /etc/hosts only,
> no DNS at all. Later with DNS it still worked without MX records but
> there were somany sites that I could not send email to.

Huhn?

All you need to send email to most/all locations is a resolvable domain
and an in-addr.

The MX is for *inbound* email.

> 
> 
>>2) The lack of an MX record seems to result in a fall-back to the A
>>record (which explains why we are getting e-mail).
> 
> 
> I see MX as kind of a CNAME record. It is an A record after all that
> says where your mail should go.

No.  If you have an MX, the MX controls the host/A to which the
email is directed.

> 
> 
>>3) I've noticed a huge reduction in the amount of "zombie" or trojan
>>spam being received by several of our well known addresses.
>>
> 
> 
> Only after I had my MX record in place and a lot of other things in sync
> with each other I was able to send email to mostly all sites.

Then you must have had a bunch of stuff hosed, because there is
no requirement for an MX record.

> 
> 
>>Because of all three of the above (especially item 3) I think I'll be
>>letting this experiment go a while longer and see if not having an MX
>>record turns out to be a great way to prevent spam from finding us.
>>
> 
> 
> It is only 3) that makes a difference. How about your outgoing mails?
> 
> 
> I can imagine some spammers digging for MX records. But they still
> must know a user. How about a user "*" that get all mail that does
> not find a valid user, and sending this mail silently to the bin?

Email addresses are easy to find or manufacture... there are lists
of typical names just like there are lists of typical passwords.

> 
> 
>>Anyone care to comment?
>>
>>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 is an anti spam wg at ripe I believe.
> 
> 
> Regards
> Peter and Karin
> 
>