How can a user put comments into rcpt to address

[K. F. Yim - Netvigator]

My users previously put comments with his recipient address. e.g.
[EMAIL PROTECTED](comments). It worked for sendmail type system for message
handling.

Now he is complaining that whenever he puts (comments) with the recipient
email address, qmail bounces.

How can I overcome this problem.

K. F. Yim