What default gateway should I use with SMTP?

In order for the SMTP to work correctly you can not have the Default gateway set to 0.0.0.0. This will work for several applications but does not work for the SMTP server. 

A default gate way on the same network was the only way it will work.

For example if my Static ip address is 10.199.7.10

I would set my default gateway as 10.199.7.1