I would like to know whether is there's a way to customize the Subject Line when we are sending the 'Forward to a Friend' email to the colleague or to the friend. Since when the email is sending to them it's not showing any indication that it's a forward email. So would like to know whether we can change the Subject Line when the email is delivering to the friend.
Well, there is no OOTB solution to achieve this IMO! This is currently in the Open Ideas state. There’s a scope to customise the FWDed email body using velocity though- refer Sandy’s blog here.
There is one way to tell.
As long as the email is not Operational, then if they’re receiving the email even though their Unsubscribed is true, that means it’s a Forward to Friend email. And you can detect that in a Velocity token and change the Subject line.