NAT Question - Why does this not work?

[Cizco]

Hi,

I have the following NAT rule for an internal server to reach an SMTP server:

nat (inside,outside) dynamic interface

If I change the above to the nat rule below, email is not sent:

nat (inside,outside) static interface service tcp smtp smtp 

Why would the second rule not work? Is it not doing the same thing (including also allowing a bi-directional connection)?

[Mohammed al Baqari]

run packet trace and see what is happening with 2nd rule.