What's that thing called where I can input email#sometopic@example.com where it is either still sent to the main inbox or sent to a folder sometopic, depending on server settings? I am having trouble searching for it, though both gmail and other email providers observe it.
It's a mailto URI extension. I don't know if it has a specific name or a standard attached to it.
A SMTP server can do whatever it wants with the mail that is delivered to it. When you send mail to anystring@domain.tld, it is delivered to the SMTP and then the server can process that anyway it wants. For example, some servers treat that string as case senative, while to others they are the same.
I don't know if a hash (#) is allowed in that string under the mailto scheme. You can look it up in the RFC (RFC 6068).
But otherwise, the server can do what it wants and sort and file and process that string (and the message that came with it) to its hearts content.
