Just a heads up in case someone else comes across this issue. I have several forums which use separate Google Apps accounts for email. A couple of months back I set up the Automated Bounced Email Handler on two of my forums. One worked fine - but the other one kept getting server errors indicating that it could not connect to the mailbox. I checked the settings over and over and they were basically identical to those on the other account (other than username and password), so I couldn't work out why one worked and the other didn't. Yesterday I had cause to log into the bounced email account directly in Google Mail - discovered a heap of messages: Subject: Sign-in attempt prevented Hi _____, Someone just tried to sign in to your Google Account ________ from an app that doesn't meet modern security standards. Details: Monday, 9 November 2015 22:25 (Japan Standard Time) Japan* We strongly recommend that you use a secure app, like Gmail, to access your account. All apps made by Google meet these security standards. Using a less secure app, on the other hand, could leave your account vulnerable. Learn more. Google stopped this sign-in attempt, but you should review your recently used devices After scratching my head for a bit, I remembered a setting in the Google account profile which mentions "less secure apps". Go here and log in with your Google account settings: https://www.google.com/settings/security/lesssecureapps ... and turn ON "Access for less secure apps" More information: https://support.google.com/accounts/answer/6010255?hl=en-GB Works like a charm now!