Can only send small messages but can receive anything... 1

[guido45]

Hi

A client of mine is having problems with his Exchange server (5.5 SP4 on WinNT4 SP6) - he is able to send very small emails (one or two words) but anything larger than that sits in the outqueue and generates a NDR after 72 hours.

He has tried sending via his ISP's SMTP and through DNS. He also set up Exchange on two different servers (both Win2k) with all the same mailboxes etc and still had exactly the same problem.

He has no restrictions on sending emails and the stores are small - priv.ebd is around 600Mb and pub.edb is only 3Mb

His ISP says that this is not their problem - they can see the exchange server begin to send the "large" emails and then skip to the next one before it is complete...

Please help!!

 

[dennisbbb]

This is an Anti-spammer scheme.

His ISP is using a packet sniffer on smtp packets, stopping almost all messages, except the "close to 0 byte" messages. The closed to 0 byte messages can slip thru the sniffer due to the relatively slower sniffer service. You cannot change ports and bypass this sniffing since it looks at smtp signature.

Your only option is to use their smtp server to send email, and use your company's server to receieve email.

 

[guido45]

Would this also affect him if sending via DNS?

He says he's tried both that and through their SMTP server but has problems either way...

 

[guido45]

Turns out they had a new firewall which was configured by the supplier and it was preventing emails as described in Dennis' post

 

[dennisbbb]

Further testing leads me to believe this is in fact a new type of spam prevention method by ISPs trying to stop spammers from using their resource. They use this sniffer to prevent all their users from implementing a spam operation using their lines. The side effect is, users will now have to use their smtp servers to relay mail to their company mail server.

Note this sniffer operates similarly to the packet sniffer of Instant Message and Gnutella (Kaaza, Limewire, bearshare ) packets, by throttling down connection speed down to almost 0 kbits/s.

 

[dennisbbb]

And good thing you found the cause of your troubles. Thanks for the star!