Topal — Features

Topal is a ‘glue’ program that links GnuPG and Pine/Alpine/Re-Alpine. It offers facilities to encrypt, decrypt, sign and verify emails, including inline OpenPGP, MIME/OpenPGP and S/MIME. It can also be used directly from the command-line.

Multiple inline PGP blocks can be processed in display filters.
Decryption and verification output can be cached to reduce the number of times a passphrase is entered. This also helps when secret keys aren't always available, at the expense of storing decrypted output.
MIME/OpenPGP (RFC2015/RFC3156) multipart messages can be sent and received. Depending on configuration, this might involve procmail or patching Alpine.
The deprecated application/pgp content-type can be sent and received.
S/MIME messages can be sent and received if gpgsm is available. (openssl is also used in some circumstances, but gpgsm is still required.)
Topal can be used as Alpine's sendmail-path command.
Topal has a remote sending mode (a server and a means of accessing the server) for reading email on a distant computer via SSH with secret keys on the local computer.
A range of mechanisms for selecting keys for both self and recipients.
There is a high level of configurability (although the configuration interface does not expose all of it; you'll have to edit .topal/config).

See the documentation in topal.pdf for further details.