OK, then Google is likely to be stopping you from logging in because it is considered to be insecure - they no longer allow the use of the "Less secure app access" setting to avoid this, they disabled it recently.
Do the following:
Login to the account in a browser
Go to https://myaccount.google.com/u/3/security
Go to the 'Signing in with Google' section and enable 2FA
Once enabled, you will then have an entry titled 'App passwords' - click it
Change the 'Select app' entry to 'Mail
Change the 'Select device' entry to 'Other (custom name')
Click 'Generate'
Use that password in your IPS email configuration instead of the main account password
Veritas Roleplay got a reaction from tnn in Issues with mailing settings
Veritas Roleplay got a reaction from Nathan Explosion in Issues with mailing settings
