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+Leap SMTP Gateway
+=================
+
+The Bitmask Client runs a thin SMTP gateway on the user's device, which
+intends to encrypt and sign outgoing messages to achieve point to point
+encryption.
+
+The gateway is bound to localhost and the user's MUA should be configured to
+send messages to it. After doing its thing, the gateway will relay the
+messages to the remote SMTP server.
+
+Outgoing mail workflow:
+
+  * SMTP gateway receives a message from the MUA.
+
+  * SMTP gateway queries Key Manager for the user's private key.
+
+  * For each recipient (including addresses in "To", "Cc" anc "Bcc" fields),
+    the following happens:
+
+    - The recipient's address is validated against RFC2822.
+
+    - An attempt is made to fetch the recipient's public PGP key.
+
+    - If key is not found:
+
+      - If the gateway is configured to only send encrypted messages the
+        recipient is rejected.
+
+      - Otherwise, the message is signed and sent as plain text.
+
+    - If the key is found, the message is encrypted to the recipient and
+      signed with the sender's private PGP key.
+
+  * Finally, one message for each recipient is gatewayed to provider's SMTP
+    server.
+
+
+Running tests
+-------------
+
+Tests are run using Twisted's Trial API, like this::
+
+    python setup.py test -s leap.mail.gateway.tests