MIME types can be associated with an external program to be viewed. This is done in the database through the programs table.

File extensions may be associated to programs through the operating system. When an attached file has an extension registered in the system, the contextual menu on that attachment has an Open with: name of program entry. Also when double-clicking on the attachment, an Open or Save choice is proposed in a intermediate dialog box. Currently, this association between file extensions and programs is only checked on the Windows platform.

Attachments of type message/rfc822 are displayed by default in a window inside the interface, but if a program is assigned to them, it will be run instead.