Make Decrypt Keys List
Once you could decrypt a message, you can make a list of the decrypt keys.
Put the sender name into the sender which is the bottom part of Mail Reader, and click "Put into Decrypt Keys" button. (below image)

How to use Decrypt Keys List

When you receive an encrypted mail from the same sender, you do not need set the cipher names and type the cipher password.

1) Copy an encrypted mail message in a mailer you received.

2) Put the password of "Decrypt Keys" and open a Decrypt Keys list window. (above image)

3) Select a sender name and click on "Set" button or double click the name.

4) Close "Decrypt Keys" window and double click on the "Decrypt Panel".

Mail reader and Image Viewer open immediately.