Migrating SMTP server ... no problem

In the process of migrating the SMTP server to the cloud or another server, it can be painful to go around change smtp server in all printers, scripts, SNMP servers .... assuming some of them take only IPs and not hostnames.

I found this amazing tool to use in the interim phase until officially moving to the new server.

RINETD is very handy to redirect a connection to a certain port to a different machine and port.

http://www.boutell.com/rinetd/

At the final migration you can use a router or firewall to translate the IP of the old machine to  the new server.

ASA syslog ID 419002

Duplicate TCP SYN from inside:source-ip/source-port to inside:dest-ip/dest-port with different initial sequence number

After spending an hour looking at this and capturing traffic, turns out to be a routing problem.

Just thought I put this out there, might help someone.