I thought that at first, however the response from the request that retrieves that information returns the correct username:
“mailUsername”:"sentry@mydomain.com"
The configuration, as I have shared above, seems to be correct, and sentry.conf.py does not have any line relating to email since I am using the default one, provided in version 10 on the onpremises github repository.
There is also no other Env. Var on the docker compose relating to SMTP configuration.