Add x-postguard header to encrypted emails

[rubenhensen]

Cryptify should add an x-postguard header to encrypted emails when sending.

Why

The Outlook add-in uses the OnMessageRead launch event (Mailbox 1.15) to automatically decrypt emails when they are opened. This launch event uses HeaderName="x-postguard" filtering so it only fires for PostGuard-encrypted messages. Without this header, the launch event never triggers and the Outlook add-in cannot auto-decrypt.

What to do

When sending an encrypted email via SMTP, add the x-postguard header (e.g. with value 0.1.0 or the current version) to the outgoing message headers.