Upgrade to 4.0.
The major changes compared to the IMP 3.x versions are:
* Much improved message format support through Horde's rewritten MIME
* Many, many additional and improved mime viewers for attachments.
* Encrypting, signing, decrypting and verifying of signed and encrypted
messages (PGP/GPG and S/MIME).
* Message filters moved to a separate application (Ingo) to support more
filter backends and a more robust/comprehensive/easy-to-use UI.
* Full charset support in folders, mailbox, message and compose views.
* Mail folders in the left menu.
* Experimental support for virtual folders.
* Preview of attachments in compose view.
* Send attachments as links.(Only the first 15 lines of the commit message are shown above )