SMTP Virtual Server - delayed delivery to certain domains

When sending mail to certain domains (mostly yahoo.com), the message may be delayed for an hour or more (sometimes alot more).

The messages show up in the smtp que immediately and the que folder state is "active".  If  I do a find on the messages in the folder, their state is "queued".  They will eventually be delivered.

This seems to be an intermittent problem so I suspect external problems but have had   a few other domains recently with the same problem.

I have done the telnet test from the Mail Front-End server to the problem domains mx servers and it works fine.

Searches for solutions has taken me to antivirus (Trendmicro), EDNS (turned off), reverse dns entries, etc...

I did a packet sniff on the server segment and it doesn't seem to be trying to send out the messages even though everything looks like it should be (que active and messages queued).

Thanks for any help you can give.
swosuwebAsked:
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r-kConnect With a Mentor Commented:
Does Message Tracking help?

I am not sure, but this could be due to certain sites delaying accepting delivery from you if they think you may have sent them spam in the past. A legit server will try again after some time, so they reject the first atempts.
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metaljoe_xpCommented:
I'm having the same problems on a 2 week old install of Exchange 2003, as well as this error: There was a SMTP communication problem with the recipient's email
server.  Please contact your system administrator.
    <mail.domain.com #5.5.0 smtp;550 No such user - psmtp>

I think they are somehow related, other posts claim that masquerade domains seem to resolve it, but I don't get it.  Again other posts claim that "Send HELO instead of EHLO" fixes this problem, but still no luck for me...  I'd love to know what to do to fix this and will reward all of my 525 points to the one who resolves our problems.

Joe
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SembeeConnect With a Mentor Commented:
Greylisting seems to be causing some of these problems. The implementation of greylisting seems to vary in its effectiveness, with some sites not getting it right. The idea of greylisting is, as already said, to weed out legitimate email from spam. Spammers will try once and not again, legitimate email will try again. However it does depend on the SMTP message that is returned to the sending server and how it interprets that message.

Masquerade domain will not do anything to resolve the problem. That just indicates another domain for the NDR messages. Click Help on that screen and it will explain it all.

If you are having problems with certain domains, then after checking your DNS, reverse DNS and server banner is correct, you may end up having to use an SMTP Connector to route email through your ISPs SMTP Server.
http://www.amset.info/exchange/smtp-connector.asp

Simon.
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