Fastmail also supports subdomain addressing for your own domains so that if your email is user123@yourdomain.tld you can use whatever@user123.yourdomain.tld rather than user123+whatever@yourdomain.tld and it will be delivered to your mailbox. This is great because:

1. You can create a new alias spam@yourdomain.tld and sign up for services with whatever@spam.yourdomain.tld and it’s all centralized in the same inbox.

2. I’ve found some websites that don’t allow ‘+’ in their email checker/parser. Also since plus addressing is such a common pattern, when sites sell your email to marketers, they probably strip the ‘+whatever’ part anyway so you’ll never know who’s selling your info.

3. They make it really easy in the web UI to reply to emails sent to whatever@user123.yourdomain.tld from the same email address (whatever@user123.yourdomain.tld) vs. for example if you use wildcard addressing. I’ve found this helpful for the few times when an automated email system or customer support person requires you to reply from the correct email for “authentication”.

Awesome! I didn't think they supported this the last time I looked and its the only thing that was stopping me from migrating