[Dovecot] dovecot.index mtime

[Matt]

Is there anyway I can get Dovecot to update mtime on dovecot.index
everytime a user successfully checks there email?  Or perhaps there is
a better way to do what I want here.

I am working on a script that I want to check when the last time a
user checked there email account.  If a user has not checked it in say
6 months I want to automatically suspend the account through the MTA.
If they start checking it again I also want to automatically reinstate
it.  What I thought was a good way was to look at the mtime on
dovecot.index but a user can be checking there email daily but if they
do not receive a new message in say 6 months the mtime will date back
to 6 months still.  Ran into this with an email address used by a fax
machine.

So is there a better way with dovecot to determine this?  I am using
dovecot-1.0.rc29 right now.

Matt