Hello! I have a problem with a slow SMTP connector between a exchange 2003 and a exchange 2010 environment, the mails are placed in que and there after they are moved to the Messages with an Unreachable destination queue and there after sent to the exchange 2010 environment. I turned on logging on the exchange 2003 queue and the only message I see is 421 4.7.0 Too many errors on this connection closing transmission channel. I can telnet the 2010 environment but its quite slow Any ideas? Magnus

SMTP Connectors have nothing to do with the communication between Exchange 2003 and 2010 on the same domain. Routing Group Connectors do that. Therefore if you are using an SMTP Connector then you have things setup incorrectly.n This sounds like interference of the SMTP traffic stream. Firewall, antivirus or antispam software would be the primary suspects. Simon.Simon Butler, Exchange MVP Blog | Exchange Resources | In the UK? Hire Me.

SMTP Connectors have nothing to do with the communication between Exchange 2003 and 2010 on the same domain. Routing Group Connectors do that. Therefore if you are using an SMTP Connector then you have things setup incorrectly.n This sounds like interference of the SMTP traffic stream. Firewall, antivirus or antispam software would be the primary suspects. Simon.Simon Butler, Exchange MVP Blog | Exchange Resources | In the UK? Hire Me.

Sorry we have been migrating between two forest, the Exchange 2003 is in the source and the Exchange 2010 is in the target forest

The rest of my response still stands - it sounds like SMTP interference. Simon.Simon Butler, Exchange MVP Blog | Exchange Resources | In the UK? Hire Me.

Do you have only one SMTP connector in exchange 2003 ORG? What about other SMTP connector behavior for different address space. Its looking me DNS look up issue for your exchange 2010 user. Anil MCC 2011,ITIL V3,MCSA 2003,MCTS 2010, My Blog : http://messagingschool.wordpress.com

hi, I also recommend that you should check your firewall and any spam protection software as well. If you have any update, please post here. thanks,CastinLu TechNet Community Support