[Dovecot] post-login scripting using PHP

I'd like to write post-login script using PHP. I noticed every shell post-login script ends with: exec "$@", which effectively executes dovecot's script-login.

However, while I try to do the same (?) in PHP: $prog = $argv[1]; exec ("$prog"); it doesn't work. The client timeouts, dovecot (2.0.6) says "Disconnected for inactivity".

May be I don't clearly see the way post-login scripting should work. Any hint to make it done?

Regards,

MU