Telnet from non-primary Interface
To test outgoing connections from a system with multiple IP addresses, the best tool I have found is netcat. It allows you to craft and monitor traffic as well as telnet from the non-primary IP address. I use netcat to test outgoing connections for qmail patched with outgoingip.
To telnet from a different IP address, just specify the address on the command line:
netcat -s 188.8.131.52 -T smtp.mailserver.net 25