Rated 5 out of 5 stars
Welcome revival of DropBox addon.
If you do Dropbox, I do recommend this. It automatically offers to convert outgoing attachments, whose size exceeds a configurable threshold (default 5MB), into cute-looking links to files in your Dropbox share, appended to the message's text. The outgoing email travels swiftly and cleanly to your recipient, without any faffing about copying/pasting links etc.
Sufficiently simple to use, I hope to persuade my MD to use it, and thus stop filling his copy-to-self IMAP folder with giant attachments.