> And if you know that, you can both know that facebook.com@mydomain.com is also me, and that you can send me an email at whatever@mydomain.com to also reach me

> And if you know that, you can both know that facebook.com@mydomain.com is also me, and that you can send me an email at whatever@mydomain.com to also reach me. SimpleLogin for a custom domain uses MX, SPF, DKIM, and DMARC records to help protect you. Yes, if someone does a reverse lookup they can detect that you are using the service, but if you are using an email forwarding service they can more easily detect the provider. I find it very rare for anyone to actually check the records. With their custom domain service you can also use a subdomain, so instead of polluting your bare domain, you can create a unique subdomain for email addresses. You can also use random aliases, so the addresses are not easily guessable (at all). > Whereas if my email address is, say, sd4k23@mozmail.com, then you can't know my other random aliases, while I'm still able to see who I gave that email address to via the relay.firefox.com dashboard. No, but then I know the entire mozmail domain is shared and so spammers will target it more frequently. > Note that I'm not saying you should switch to a service like this; I'm just trying to show why I've started using both: my custom domain for sensitive services, and Relay for one-offs/few-offs (e.g. if I just want to get a coupon code or something). I can agree there, if you are just creating temporary emails that you don't care if you lose then an alias-provider domain is fine. However, like most people the risk is that they either don't use an alias for other services that are more important or that they do and then the provider shuts down and they can't verify their account.