Launchpad - Sending Domain support

We've added the ability to use your own sending domain in Launchpad!

This is great for those of you who are using a custom domain for your emails. You can now use your own sending domain for your Launchpad campaigns.

As part of this, we also added one-click unsubscribe headers to your campaigns, to comply with GDPR and CAN-SPAM laws.

- Ashley