Re: DNS Lookups

[web400@xxxxxxxxxxxxxxxx]

> Why would you ever do step (a)? The existence (or non-existence) of an A
> record for techsoftinc.com has no bearing on where our e-mail goes --
> and in fact, it doesn't even go to us at all.

Why would you do step (A)?  Because not everyone uses your particular 
domain, or sets theirs up the exact way that you did it.

I can have a domain that has absolutely no MX records. (It's perfectly 
legal, and works perfectly fine.)  In that case, it's the A record that 
determines where the mail gets routed to.

When an SMTP program sends e-mail, it tries the A record first -- that's 
why I made it step A... because that's how e-mail works.  When that fails, 
it goes to the mail exchangers (MX).

> All our mail goes to postini for spam/virus filtering and then on to our 
> Exchange SMTP servers. And the A record for techsoftinc.com points to an 
> entirely different location than our SMTP servers.

That's nice, but Jon probably wants his software to be able to send mail 
to other people aside from you.

> Also, don't forget, it's perfectly valid to have a domain for e-mail
> that has no associated A record. Take us.ibm.com as an example.

Yes, that's why when step (A) fails, you go on to step (B) and look up the 
MX records.