Fastmail lets you convert myusername@fastmail.com to whateverwebsiteorservice@myusername.fastmail.com It's not a literal alias, but it works out fine. One of

Fastmail lets you convert myusername@fastmail.com to whateverwebsiteorservice@myusername.fastmail.com It's not a literal alias, but it works out fine. One of these days I'm going to propose the Thunderbird + K-9 mail addons that say 'set the sent from email address to be equal to the sent to email address', that way if service@myusername.fastmail.com is the recipient, it will be the sender to any replies, rather than the MUA default replying with myusername@fastmail.com (but that's a separate discussion)