Can't receive some bounce messages

[sami_c]

Hi,
I'm using a php script (on a debian server with posftix) to send emails. I receive bounce messages in my www-data file. However mails sent to some invalid emails (that I know) are not in the www-data file !!! I'm sure those emails are invalid because I tried ti send them en email via my gmail account and I received bounce messages! What coud be the problem with postfix ?
Thanx

[Google]