Outbound SMTP mail problems

[Barkey]

Since Monday we've noticed severe delays when sending
mail. Items enter the queue under the SMTP virtual
server, yet take hours (some days) to actually be sent.
There are no problems however, with inbound mail.

Emials without attachments sent to a particular domain go through just fine. When a mail with an attachment is sent, it clogs the connector and all mails queue up behind.

System is W2K SP4 with Ex2K SP3

DNS looks to be working OK. Example

http://www.yahoo.com

resolves correctly.

Taking a particular domain for which mail is queued, it
is possible to telnet onto port 25 of a the destination
domain, so we know connections are possible.

We've reapplied Win SP4 and Exchange SP3 just in case,
with no avail.

Having set up all the error reporting, errors in
application log are:

Source: MSExchangeTransport
Category: Connection Manager
Event IP: 4000

Description:
Message delivery to the remote domain 'hotmail.com'
failed for the following reason: The connection was
dropped by the remote host.

Any Ideas.... Please Help!!!

 

[joeschoe]

Could someone have sent spam via your server causing you to be blocked by hotmail?

Do you have a virus checker scanning all outgoing mail. This can cause delays which generate a time-out in the communication

 

[Barkey]

No sign spammers using server. Certainly not set up to relay!!! Did however check black lists as part of our troubleshooting and we were not listed in any way. It is not just Hotmail but all domains where an email is sent with an attachment... this blocks the queue.

For instance, I can happily sent plain text emails out to joe@test.com, but when a mail with an attchamnet is sent, it is delayed in the queue. This then delays all mails behind it.

Did follow path of AV getting in the way. Disabled all Exchange AV software, but this made no difference.

Another thing we tried was adding PerMsgFailuresBeforeMarkingAsProblem entry to the registry (

http://support.microsoft.com/default.aspx?scid=kb;en-us;308350

)but again no difference.

We are really struggling on this one now!!!

 

[kbullit]

Have you tried to manually connect to any of the domains that you're having problems with? If you'll set local echo and determine what type of replies your getting back from the other end it may help you figure what the dropped connections are for.

If you're not familiar with connecting to those servers manually you can use the following article as a how to.

Microsoft Knowledge Base Article - 313395

 

[xmsre]

Anything in between that could be losing the connection? Squid on Linux? Changes at the firewall?