SMTP Outbound Emails show Error 500: Unkown Error

[RedPepper]

Hello,

We recently installed a docker container for EspoCRM. It looks like a solution that fits our needs.
However, when we try to enable Outbound Emails under Administration > Outbound Emails, we get Error 500: Unknown Error.

We've tested multiple domains (gmail, company, personal) and all errors are the same.
Since we want to use EspoCRM for our company I'd like to focus on that solution which includes 2FA.

We've created a new account in our MS Tenant, when through 2FA setup, and created an App Key which is currently set as the password under SMTP.
We can see the server connecting to the outside world in our Firewall over the correct ports, but still Error 500: Unknown Error is shown.

This is what I gathered from the logging:

<IP of our host> - admin [20/Jan/2025:15:33:19 +0000] "POST /api/v1/Email/sendTest HTTP/1.1" 500 289 "https://espocrm.domain.topleveldomain/"; "Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:134.0) Gecko/20100101 Firefox/134.0"

Please note I removed our IP-address and domain for privacy concerns.

We are running on version 8.4.2

Any tips in resolving this issue?

Thanks in advance.

[RedPepper]

Update: I managed to get this to work by using an external SMTP provider (SMTP2Go) after finding out Microsoft has/is going to depricate SMTPAUTH. I think this might cause issues for a lot of users in the near future (september 2025). Is espoCRM aware of this?

https://learn.microsoft.com/en-us/exchange/clients-and-mobile-in-exchange-online/deprecation-of-basic-authentication-exchange-online