i'd be surprised if theres a program that could do this. the subject is just part of the long data stream that the server sends as the 'email'. like heres how a typical smtp session goes when server A is sending a message to server B
1. server A: Hi
2. server B: Hello
3. server A: I have a message from
spamuser@spammyspam.net (envelope from)
4. server B: ok
5. server A: The message is for
innocentuser@yourdomain.com (envelope to)
6. server B: ok give it to me
7. server A: Date, Time
From
To
Random Header
Subject
Body
DONE!
Now at any point in steps 1 through 6 your server can terminate the connection. Like you'll se mta blocking based on ip blocking or the envelope from which would cause your server to just say like "I don't trust you I don't want your e-mail" but once your server says "give me hte message" its not going to do anything with what it gets until the other server says it's done.