[Dovecot] Post-login scripting - Trash cleanup

[list at airstreamcomm.net]

We are considering using the post-login scripting to clear trash older
than 90 days from user accounts.  has anyone done this, and if so did this
cause logins to slow down too much waiting for the trash to purge?  One
idea was to execute the trash purge script once a day by tracking their
logins and seeing that it has already ran that day.  Another idea was to
call the trash purge script in the background and continue without
acknowledging that it has finished to keep logins speedy.