other smtp server unknown gmail server

Hello! I randomly found, while changing some settings in one of my mail accounts, a smtp gmail server with a gmail address that is not mine. The server was listed under "other smtp servers" and it was set to OFF. I have no idea how it got there as I have 2 factor auth on for all my mail accounts and also for apple id. I don't give my phone away and I don't click links or ads on websites. I try to stay as safe as possible in my online activity.

Does anyone have any idea how it could have got there? Because I certainly have no clue. Also, what does the other smtp servers actually do if they are turned on? Trying to figure out what could have been compromised.