Yeah pretty much, its a way to sending and receiving emails without giving out your real email address. Instead you give aliases than end with “@simplelogin.com”, to protect your privacy and which are then forwarded to the email you provide to simplelogin. The received emails have a different sender address, for instance instead of [email protected], you see: the forums_at_macrumors_com_randomcharactershere@simplelogin.co.

You can actually reply to forums_at_macrumors_com_… and simplelogin will forward the email.