Sorting emails

I have written a patch which lets sort emails based on date/subject/sender/size.

Sort is using php imap library sort feature, which from the first view might seem strange since, for example, if you sort by sender it will sort by email address, not sender's full name in the From field. Similar for the subject - it drops RE: suffix and then sorts.

I'm using courier imap server. Not sure how php imap library sort function works with other imap servers or is this server independent?

To improve the sort we would have to cache message's headers in the database and then perform sort in the database query. Don't how to implement sync between cached and latest messages. Caching all headers on each page request would put a lot of load to the database.