I own several domains where I don't have separate mailboxes or mail user accounts. To receive mail, I've just setup a catch-all for such a domain that redirects to a generic address elsewhere.
Now, I want to add firstname.lastname@example.org as my address in Gmail (as an alias), so I can send mail using that as From-address. In the past I could simply add it, click a confirmation link, and done.
However, it seems that Gmail demands an SMTP server + user account for that domain!? I don't have that. And even if my domain would come with an SMTP server, I still don't have a mailbox or user account (since I only use email forwarding on that domain).
How do I setup Gmail so I can send mails from my custom mail address, which I do own, but for which I don't have an SMTP server or account?