DEVONthink lets you archive emails or send documents via email directly from your databases.

Get your emails into DEVONthink from Apple Mail, Microsoft Outlook, or any email applications using standard Unix mailboxes, e.g., Thunderbird. You can even set a hotkey to archive messages and mailboxes while in Apple Mail and Outlook. With its hierarchical groups structure, classification feature, and powerful search engine, DEVONthink is perfectly suited for adding, sorting, and finding emails in your databases. And attachments can be imported automatically or on demand.

You can also use the Send by Email command in the Data or context menu to create a draft email with a selected document attached, provided you're using a compatible email applications. And of course, you can drag and drop from your database into an email you're composing.