I used to use the "send mail as" feature so I could use the gmail interface for my work emails instead of outlook. My workplace has now mandated 2-factor authentication for their single-sign on, so when I go to add my password in the SMTP configuration, I get an Authentication Failed error because I don't have the opportunity to add the second factor. Is there a way to get around this?
Question is a bit old, but I believe the answer is you need to create an App Password for the account you want to use as an alias. E.g. you have two email accounts email@example.com and firstname.lastname@example.org. email@example.com has two-factor authentication. You want to be able to send emails from firstname.lastname@example.org as email@example.com. Set up an App Password for firstname.lastname@example.org using these instructions. Then when you're asked for a password for email@example.com in the "Send mail as" dialog box, use this app password.