i test yesterday a configuration like you see in the image attached.
If you use the public address for the SMTP Profil 1, then everything work, but if you use the internal address over the IP-Sec Tunnel, you have every time this error message:
2013:04:29-13:35:00 firewall-1 exim-out[20785]: 2013-04-29 13:35:00 1UWm1m-00056B-BL SMTP timeout while connected to 10.12.0.2 [10.12.0.2] after sending data block (8189 bytes written): Connection timed out
2013:04:29-13:35:00 firewall-1 exim-out[20784]: 2013-04-29 13:35:00 1UWm1m-00056B-BL == info@poi2.com R=static_route_hostlist T=static_smtp defer (110): Connection timed out: SMTP timeout while connected to 10.12.0.2 [10.12.0.2] after sending data block (8189 bytes written)
i think here is a but in the smtp proxy ...
you can download and upload file from and to this server, open the owa and so on. But only the smtp proxy don't work correcly. In the Firewall log is nothing and the IPs is turned off.
kind regards