There's no setting in SmarterTrack that limits attachment sizes. However, there is a hard code limit of 100MB for any ticket submitted via the Portal. There's no limit in SmarterTrack, that I'm aware of, for limiting attachment sizes pulled in via POP or IMAP, though.

That said, your email server will have file size limitations that would impact the attachment size prior to a message being pulled into SmarterTrack.