Messages aren't imported or can't be filed: Email messages are imported with a special identifier (UUID) that helps DEVONthink keep track of messages that have already been imported. Since a UUID must be unique, you can't have more than one file with that identifier. If you try to import the same message into a database, you will receive a logged message stating "n emails already imported".

Importing takes a long time or stalls: Importing email is not a trivial process. Not only does it copy the message into your database, but it also reads and analyzes the entire contents of each one. If you are importing a large mailbox, the process could cause a timeout.

To increase the timeout to five minutes, please enter this in /Applications/Utilities/Terminal.app (each as a separate command) while DEVONthink is not running:

Another possibility is to split the mailbox into multiple smaller ones. Lastly, you don't have to import the entire mailbox at once. Importing smaller batches often proves to be less taxing on the machine's resources.

Why can't I import from email application X?: Inter-application communication, something at which DEVONthink excels, isn't universally developed. In order for more true automation between applications to occur, the developers need to implement robust and reliable mechanisms, like AppleScript. Some apps may provide simple URL schemes but they are limited in use and capabilities, often only able to process one file at a time. Better results can usually be had by merely dragging and dropping. For email clients with a good AppleScript dictionary, the potential for streamlined workflows is increased.