That's not relevant for the discussion in this thread where we already assume you have a custom domain with catchall inbox setup. The custom From is still needed to be able to actually send from any address on that domain.

Yes, and part of that setup is proper sfp setup? Eg allow sending from Gmail with a from on your domain?

I don't see how it's specific to sending from thunderbird. It's a general issue if you want to use a domain for mailing.

It's not spesific to the mua, no. But as thread starter (ed: first responder) said:

> Word of advice for anybody doing this: make sure you have a way to SEND email using one of your aliased addresses

So a) you need a mua like thunderbird that let's you set FROM header - and b) your domain need to be setup to allow your smtp server(s) to send from your domain (sfp).