Does SquirrelMail actually flag mail as read by updating the mail record?

I ask because I think some mail readers don't seem to fetch email which has been opened in squirrelmail? I have a user who can't get his email but has problems with his pc and has been using squirrelmail in the meantime to view incoming mail and now can't fetch his email so I'm not sure if its his pc setup or because the mail has been flagged as read.

sorted. User hadn't told me they were using a new email client and set "leave mail on server flag" to on.