The Recipient Filter page of Mail Options contains settings that control how Smartcrypt Attachments handles certain recipients.
Never Encrypt list
There will be people you correspond with that will never see sensitive emails or attachments from you. Add their email addresses to the Never encrypt when sending only to these recipients list. Smartcrypt will not prompt you to encrypt for these addresses.
Be aware that if encryption is otherwise required for any single recipient (including inclusion on the Always Encrypt list), Smartcrypt will bypass the Never Encrypt list, and encrypt the data for every recipient.
Always Encrypt list
There will be people you correspond with that will always receive sensitive emails and attachments from you. To ensure that you always encrypt mail to those individuals, add their email addresses to the Always encrypt when sending to these recipients list.