On May 30, 2022, Google is taking away the "Allow Less Secure Apps" setting in GMail and forcing 2-Step authentication. This "Allow less secure apps" setting was set to "On" to use Gmail as the email sending server. However a better solution is available. Please follow these steps in order to use App Passwords with the GMail smtp service.
GMail Documentation
1. Turn "Allow Less Secure Apps" OFF
2. Turn on 2-Step Verification
3. Set up App Passwords
Step-by-step guide
1. Turn on 2-Step Verification
Go to your Google account and into Security
Click on 2-Step Verification in the Signing into Google section
2. Set up App Passwords
Go to your Google account and into Security
Click on App Passwords in the Signing into Google section
3. Put the generated App Password in Spire > Company Settings > Email in the Password field and Save
4. Test the email in Spire by putting your email address on a Customer record and email a Sales Order to yourself
5. Email is received