CNAME, MX , FROM address unable to deliver to verizon.net addresses

[Barry Margolin]

In article <botuon$16t7$1 at sf1.isc.org>,
ksmalley <Karl.Smalley at entwhistle.jci.tju.edu> wrote:
>We have a mailserver named: entwhistle.jci.tju.edu
>We have a cname "mail.jci.tju.edu" set up to point to entwhistle.
>Recently we have been unable to send mail to certain domains, like
>verizon.net.
>
>We can telnet to relay.verizon.net on port 25
>
>and the following works:
>
>mail from: username at jci.tju.edu
>mail from: username at mail.tju.edu  (tju.edu is a domain with MX records
>as well)
>mail from: username at entwhistle.jci.tju.edu
>
>the following does not work:
>
>mail from: username at mail.jci.tju.edu   (CNAME pointing to host)

The original SMTP specification said that CNAMEs should not appear in email
addresses.  RFC 2821 appears to have relaxed this restriction, but
Verizon's mailer apparently doesn't conform to this yet.

>mail from: username at mailbox.jci.tju.edu (no entry -- hoping it would
>do an MX lookup on jci.tju.edu)

I don't know why you would expect that.  No mailer should ever try to
deliver to a different address than the one that was actually specified.
It's never right to start removing components from the domain.

>dig jci.tju.edu MX 
>returns an MX entry which points to entwhistle.
>
>How we can keep the mail.jci.tju.edu as reply-to address and still be
>able to send mail to everyone including verizon.net addresses.

Make mail.jci.tju.edu an A record instead of a CNAME.

>If we rename entwehistle to mail.jci.tju.edu with a true A record this
>would probably work, but what would we do when we want to replace that
>machine. Would we have to give that machine the same name and IP
>address?  The point of the CNAME was to make this sort of switch
>easier. Is this possible or not?

You don't have to rename anything, just have two A records:

entwhistle IN A 147.140.9.27
mail       IN A 147.140.9.27

-- 
Barry Margolin, barry.margolin at level3.com
Level(3), Woburn, MA
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