Do you need to use different SMTP servers depending on how you connect to the Internet?

Rather than constantly editing the account properties, create a new account using the other SMTP server.

While this works well for two SMTP servers, giving you Account A - SMTP 1, Account B - SMTP 1, Account A - SMTP 2, Account B - SMTP 2, it can get unmanageable if you have too many accounts and you do need to remember to switch accounts if you reply to mail downloaded through an account using the other SMTP.

Alternately, make a copy of your profile, so you have one profile for SMTP 1 and one for SMTP 2. Both profiles will be identical except for the SMTP servers used, right down to the account names and pst's used. Switch profiles when you switch Internet connections.