By "less secure", Google means that dual-factor authentication (Oauth2) is not now enabled on the Outlook instance on your PC. Since at least Outlook 2016, Oauth2 has been built in, but it is not automatically enabled. For Outlook 2013, it is also available, but requires a Registry hack.

To enable Oauth2 in Outlook 2013:

• Press Windows, type rege, and select Regedit.
• In the Location bar at top, go to HKCU:\Software\Microsoft\Office\15.0\Common\Identity (you can paste that into the bar).
• In Identity, right-click and create a new DWORD value named EnableADAL.
• Double-click that value and set it to 1.

Then, in either version, open Outlook account settings, and try to change authentication to Oauth2, as in GMail instructions.

Due to the removal of Less secure apps & your Google Account you can not use a users login and password to access googles smtp server.

You have two sevral options.

1. Switch to using the gmail api and authorize your application using Oauth2 and store a refresh token. Make sure to set your app to prodctuion or the refresh token will expire after seven days.
2. Use xoauth2 with your request to the smtp server. You will then need to use Oauth2 to authorize the application and store a refresh token. Make sure to set your app to production or the refresh token will expire after seven days.
3. If you have 2fa enabled on that account then you can create an apps password. Sign in with App Passwords Once you have created this password you can then use it in place of the actual password in your code.