Hi Gaelius,
I hope you are getting configuration error just as Arley mentioned. Can you refer to the following URLs (https://success.outsystems.com/Documentation/11/Extensibility_and_Integration/Configure_OutSystems_to_Send_Emails
https://www.outsystems.com/forums/discussion/35624/email-smtp-imap/
https://www.outsystems.com/forums/discussion/40383/error-sending-email-with-correct-smtp-configuration/) and see whether your problem is getting resolved?
Thanks,
Ragul