OT - Sendmail Address Syntax

[Paul]

Hi

Apologies for the off topic post but I know there's lots of send mail 
gurus around and I cant find anything via google.

I get lots of email addressed to aliases like |ajshdasd at domain.com ---- 
note the pipe at the start of the address, I act as a front end relay 
for various other mailservers, and wondering if there is a way in 
sendmail to 550 reject based on an invalid address syntax? I don't 
believe | is an allowed character in an email address.

Thanks

Paul