Outlook Office 365 "Send Mail As" Email Authentication Error

My work has recently created an office 365 email account for me and I need to use this new email address as an alias for my current google email address when communicating with clients. 

I have done the following steps:

In my Gmail setting I have enabled POP and IMAP

Then under accounts and imports I selected add another email address. Here I typed in my outlook email and hit "next"

I am then asked for SMTP server, email and password. Email and password is my outlook email and password, and for SMTP server I have tried the following which I found under my "Oulook" -> "mail" -> "sync email" settings:

Server name: smtp.office365.com
Port: 587
Encryption method: STARTTLS

This has not worked and I continue to get authentication errors. I have noticed my POP options are greyed out in my outlook app. 

Any ideas?