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

[Christian Smith]

In article <dro8jf$2gem$1 at sf1.isc.org>,
 administrator at spam.yellowhead.com (John Coutts) wrote:

> The proper way is to use an "MX" record. Not all MTA's check for an "A" 
> record. 
> As a matter of fact, spam engines are more likely to use cache or "A" records 
> than legitimate MTA's. Also be warned than many MTA's block DSL originated 
> email.
> 
> Your experience seems to be quite contrary to my own. I have operated a mail 
> server for over 15 years, and the amount of work to maintain it has 
> multiplied 
> exponentially over the years. For such a small number of accounts, I have 
> found 
> that it is just not worth the effort required, and recently shut down our 
> server and moved the accounts elsewhere.


No, you do not need to have an MX record in order for e-mail to work.

For a domain, example.com, if there is an A record for that host and the 
machine at the IP address which the A record points to is configured to 
accept mail for the domain, then no MX record is required.

I know of not a single commonly used MTA which will fail to properly 
deliver mail in such a scenario, and any MTA which does fail in such a 
scenario would be in serious violation of numerous RFCs.

Nor do I know of any MTA which will refuse to accept mail from a domain 
which has no MX record but which does have an A record. Certainly some 
administrators may have configured their mail server in some fashion so 
as to reject mail from such a domain, but we can't do much to prevent 
that.

As regards MTAs which refuse to accept mail from mail servers located on 
DSL networks, I think you mean they refuse to accept mail from servers 
whose IP addresses are listed in one of several lists of "dynamic" or 
DUL addresses. Not all IP addresses on DSL networks are dynamic. Many 
DSL providers provide static IP address assignments and make sure their 
IP addresses are not listed in such lists.

And, even if he is receiving mail at a server on a dynamic IP address 
does not mean his outgoing mail is delivered from the same server. He 
may use an ISP provided SMTP server to send outgoing mail.


-- 
Christian Smith
Dynamic Network Services, Inc.