This is a common problem especially with esmtp inspection. Now cisco claims its only the extended commands that they look I have found this to blatantly incorrect through the use of a packet sniffer.
To date with many ASAs installed I have yet to figure out why it always breaks email and TAC is unable to explain why either.
I have a base config i drop into every asa and now I just turn off that inspect cause no one at cisco i have met to date wants to help figure it out so i call it broke and turn it off. Not really a clear answer but its what i have learned after some very frustrating experiences i hope it helps.