Process requires yagmail and keyring libraries imported into Python environment.

Register username and password via yagmail, which in turn processes through keyring and into the OS key system, such as Windows Credential Manager, and notes it under Generic Credentials. This only needs to be processed once to register the account information.

Utilize yagmail.SMTP() to instantiate email protocol. Note that username is stored in HOME folder.

Depending on mail setup, App Passwords may need to be utilized for access by a less secure app.

Source: https://support.google.com/accounts/answer/185833?hl=en

Another option is to enable 'Allow less secure apps' under account settings. By default, this option is disabled to prevent unauthorized access, but may be the reason for the authentication error.