Your TurnKey appliance and the included software (OTRS in this case) should be configured to send all emails via Postfix. Postfix is essentially a local MTA so it should be able to send emails OOTB. However often things get in the way and mail sent directly from your server may get labelled as spam; worse still it may get dropped completely (so you don't even see it in your spam folder). Configuring Postfix to relay emails via a (trusted) remote SMTP increases deliverability.

So if you simply want to add an SMTP relay (so your server sends email) then the best way to do that is to configure Postfix to use a remote SMTP. As you can see in the docs, it is possible to use google SMTP to send email.

I think that may allow you to circumvent what you are currently trying to configure. Although TBH I'm not sure and maybe I'm totally off the mark?! If you think I've missed your point please post back with a bit more explanation. I'm not particularly familiar with OTRS either so if you could be really clear about what you are actually trying to achieve might also be useful.

So OTRS allows you to also collect emails from a remote server? And that is where you are having the error? With your additional notes and your original screenshots, that seems to be the issue.

Unfortunately though I have no idea really so I might have to have a play with it and see if I can reproduce the behaviour. Perhaps there is something not quite right in the appliance?

FWIW I have also lodged an issue on our tracker so it doesn't get forgotten: https://github.com/turnkeylinux/tracker/issues/624

Also I had a quick google. Are you behind a firewall or a proxy? That seems to be a common cause of similar issues. Although the fact that it is saying "Auth for user failed" suggests that it may be connecting, just not authorising. Have you doublechecked your password and also ensure it's configured for remote mail connection (IIRC it should be OOTB but I can't be sure...)

Google has some fussy secure access restrictions. If your application is not compliant then you need to explicitly tell Google to relax the checks.

See https://support.google.com/accounts/answer/6010255?hl=en or https://support.google.com/a/answer/6260879?hl=en 

The link to relax the checks can be found here.

 

Ok so seeing as the problem has been resolved (and it wasn't a TurnKey bug) my inclination is to close the issue on GitHub. Although perhaps we should include those links in the OTRS appliance docs? In which case, perhaps I should reword the issue and leave it open instead? Thoughts?