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.
Mail clients approach the security issue variously.
Some automatically disable elements that are potential carriers of malicious payloads such as Trojan horses. Others go further and generate simplified HTML display, though at the expense of certain content that the user might find important. And others simply refuse to display HTML in line, requiring the user to open the message in an external browser window. Two of the programs review here, EdMax and Gaucho, can be configured to toggle HTML display on or off with a simple keyboard operation, and to warn when a message contains potentially dangerous content, giving the user the option of disabling those elements. One, TsuruKame, has an optional feature that deletes the HTML attachment part of any incoming message.