creating global rules in openwebmail

open Openwebmail cgi-bin folder (/var/www/cgi-bin/openwebmail)/etc/filter.book and add the rule. Local user rules exist in ~user/.openwebmail/webmail/filter.book

amavis - To allow only password protected archives

Add these two rules somewhere towards the end
of the list in $banned_filename_re:

# allow if it is or contains any undecipherable components:
[ qr'^UNDECIPHERABLE$'=> 0 ],

qr'^\.(zip|tar)$',  # block zip and tar (unless password protected)

Encrypting file in Linux

To encrypt single file, use command gpg

$ gpg -c filename

Enter Passphrase:
Repeat passphrase:

File becomes filename.gpg

To Decrypt

gpg filename.gpg
gpg: CAST5 encrypted data
gpg: Enter passphrase

original file is extracted out of the encrypted file