I was thinking it would be cool to be able to have an email address that is just a domain, for example if I own bobsmith.com why can't I have bobsmith.com as my email address? Why does SMTP require a username, eg bob@bobsmith.com?
RFC 5321 defines the what that address looks like. <a href="https://www.rfc-editor.org/rfc/rfc5321#page-15" rel="nofollow">https://www.rfc-editor.org/rfc/rfc5321#page-15</a>
Existing RFC's require an email address. What you are looking for would require a new RFC to have a default address for a domain and of course changes to all MUA's/MTA's.<p>I think the shortest path to make something like this would just be to have an amending RFC that includes a lookup of a specific TXT record if an email address is not present. That TXT record could have a <i>default</i> email address for the domain.
Historically, when the email protocol was first made [RFC 561](<a href="https://www.rfc-editor.org/rfc/rfc561" rel="nofollow">https://www.rfc-editor.org/rfc/rfc561</a>) in 1973 personal computers were rare and very low power. At the time, hardly anyone owned a computer on their own.<p>That said, might be cool, but good luck getting most apps to accept something without an @ as an email address