Code Crafters

Definitely do not disable SMTP authentication and be an open relay for anyone to SPAM through your mail server. It's possible that Gmail supports other security features (possibly one of ENHANCEDSTATUSCODES, CHUNKING, SMTPUTF8) that we don't, allowing an alternative to SMTP authentication that outlook is happy to continue with. However, Only Allow Secure Login forces users to use a secure login method ideally via STARTTLS with SMTP authentication so that everything is encrypted and secure.

Code Crafters wrote:However, Only Allow Secure Login forces users to use a secure login method ideally via STARTTLS with SMTP authentication so that everything is encrypted and secure.

...which was my understanding as well.

Code Crafters wrote:It's possible that Gmail supports other security features (possibly one of ENHANCEDSTATUSCODES, CHUNKING, SMTPUTF8) that we don't, allowing an alternative to SMTP authentication that outlook is happy to continue with.

Probably right, though i'm not sure exactly what that would be. I use a number of the cardinal mail services (hotmail, gmail, exchange, etc) and they all either use SMTP auth or one of the newer techs like OAuth...

Yes, I agree. None of ENHANCEDSTATUSCODES, CHUNKING, SMTPUTF8 sound like security features either. Gmail may be more trusted by some other measure though.