Gmail outbound mail requires reauthentication through Captcha
Scenario
Gmail may from time to time require the mail account to be validated periodically or after accessing from varying IP addresses.
Next Steps
Be sure to read https://support.google.com/accounts/answer/6010255 first off, as weakening security is an obvious security issue!
To enable Gmail to allow less secure mail access, it can be disabled, just login to the mail account, then load the following url: