At 08:10 29-03-2008, Henning Schulzrinne wrote:
One of the problems I have seen first-hand is "disappearing" mail.
Example: A webserver sends outbound email directly, but doesn't want
to receive inbound email. The hostname leaks and mail gets sent to
that address, based on the A(AAA) record. The mail is "received", but
disappears into some never-seen /var file. In that case, the sender
never suspects that anything is amiss; it would be much better if the
sender got an immediate "sorry, that domain name doesn't support email
I came across a few (IPv4) cases where mail and web services are
hosted by different organizations. The MX query failed and the SMTP
client did a fallback to the A RR. The mail was accepted by the host
running the web service and it "disappeared".
The above can happen when sendmail is running on the web server and
it automatically adds the domain to the list of domains for local
delivery and there's a catchall address.
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