Yes, basically you will want to turn on SRS as not doing so will often lead to rejects or forwards being flagged as SPAMs because of the SPF checks.
Also be sure that you don't auto forward SPAMs as it will probably flag your server as a spam source quite quickly.
Nowadays mail autoforwarding to external domains is a real pain and should be avoided.
If it's a personal forward to a gmail, hotmail or other account you have you should configure your external account to retrieve mails from your SmarterMail mailbox instead of the other way.
If it's a forward to someone else external account, well 1) SRS 2) Configure autoforward to skip spams.
Sébastien Riccio
System & Network Admin
https://swisscenter.com