That's the way to go. I set up a rule where everything going to *@a.mydomain.com goes into a folder which I largely ignore. Every website gets a unique prefix,

That's the way to go. I set up a rule where everything going to *@a.mydomain.com goes into a folder which I largely ignore. Every website gets a unique prefix, e.g. ycombinator@a.domain.com. The advantage of Masked Emails is that third parties won't even know about mydomain.com. The disadvantage is that you need 1Password to recall which email address you used with a particular website.