OT: Sendmail Sender Verification

[Mike Kercher]

I've been noticing more and more log entries from aol.com lately similar to
the following:

Mar 29 22:18:24 avwall sendmail[29603]: i2U4INJU029603: from=<>, size=3001,
class=0, nrcpts=1, msgid=<200403300421.XAG19946 at rly-xk01.mx.aol.com>,
proto=ESMTP, daemon=MTA, relay=omr-m11.mx.aol.com [64.12.138.23]
Mar 29 22:18:30 avwall sendmail[29620]: i2U4INJU029603:
to=<username at somedomain.com>, delay=00:00:07, xdelay=00:00:00, mailer=local,
pri=123001, dsn=2.0.0, stat=Sent

I assume that the omr- stands for Open Mail Relay or something of the sort
and I also assume that it is verifying that the email address is deliverable
prior to delivering an email from an address to the final AOL recipient.  I
suspect they are doing something like this to combat their massive spam
flow.

Has anyone implemented anything like this with sendmail.  I know it would
introduce additional network traffic, but might it be worth the trade-off?
Thoughts?

Mike