Unable to send Outlook.com Email from Gmail using SMTP

I have had an email with Microsoft for several years. My original email address was @hotmail.com, which was then changed to @live.com, and is now @outlook.com.

Since the creation of my Hotmail email address, I have been using my Gmail account to manage my email - nothing against Microsoft, but I prefer the filtering and folder creation in Gmail over the various Microsoft web apps for email.

Until recently, I was able to send email in Gmail using my @outlook.com address over SMTP.

For the last few weeks, I have been receiving the following error when attempting to send mail over SMTP for my @outlook.com account using the Gmail web app. Screenshots below:

Can you please advise why this error is occurring and what needs to be done to correct it?

Thank you.