Turn off the prompt that appears before an S/MIME or a PGP protected
message is cut short
On the home screen or in a folder, click the Options icon.
Click Security > S/MIME or PGP.
In the General section, change the Truncation Mode field to Send Anyway or More All And Send.
key > Save.
To turn on the prompt again, change the Truncation Mode field to Prompt User.