The most helpful interfaces let you create rules based on actual messages. Some also have provision for creating new folders when you create a new rule. A remote mail interface lets you look at the headers of mail on the server without actually downloading it, and perform operations such as deleting mail from the server, downloading without deleting, or downloading and deleting from the server. Of the mail programs supporting this feature, some require downloading headers anew each time, while others retain the server list. TsuruKame is unique in updating the server list automatically each time it checks for new mail.
Programs differ in the way they store downloaded messages.
Some store messages for each folder in a single file, which can grow to enormous size over the years. A few store individual messages as separate files, which tends to be inefficient. Others store messages in files of a designated size, starting a new file when that size is reached. The ability to purge the message store, or to back up message files automatically, further distinguishes different mail programs, as does the degree of user control over these parameters. The ability to display HTML message in the message window or preview window is a feature shared by many of the programs reviewed here, but they differ in many significant ways.