regexp looking for email addresses in iRule

I figured out my issue. My understanding of what was vaguely written in the manual led me to the following, which got past the hanging of the SMTP session on first connect (waiting for the 220 on client_accepted):

   
 when CLIENT_ACCEPTED {  
    TCP::collect  
    TCP::release  
 }  
 when CLIENT_DATA {  
    if { [regexp -nocase {mail from:} [TCP::payload]] } {    
       TCP::respond "554 Message Rejected\r\n"  
       reject  
    } else {  
        Release the current payload onto the server   
       TCP::release  
        But still collect the next data from the client   
       TCP::collect  
    }  
 }  
 

If my logic is correct (oh, and I have doubt!), I added in the TCP release in the CLIENT_ACCEPTED because I don't really care to collect any data at that point in the very initial SMTP connection (I just want a 220 to begin sending) but from reading parts of the manual you need to start a collect in that area in order to process more CLIENT_DATA in other areas (rcpt to, mail from). So, that cured the hang and allows the session to move on.

Anyway, works quite well. Thanks for all the pointers.