Emails not working at all.

When attempting to send emails through the system using various SMTP configurations (self-hosted SMTP server, G Suite SMTP with app password, and Mailjet), none of these options successfully deliver the emails. With Mailjet, even though all settings and domain verifications are completed according to the documentation, emails still fail to send. The system shows an "ERROR" status for the email, but Mailjet does not log any attempt to send the email, indicating that the issue might be with the system's integration with Mailjet.

To Reproduce
Steps to reproduce the behavior:

Configure email sending in the system settings.
Attempt to set up a self-hosted SMTP server.
Attempt to set up G Suite SMTP with app password.
Configure Mailjet with all verified domains.
Send a test email and check the email status in the system and Mailjet dashboard.
Expected behavior
Emails should be successfully sent via the configured SMTP provider, and Mailjet should log the email-sending attempt.

OS: [server hosted on Heroku JVM]
Version: [ 2.0 - M5 ]

Additional context

It seems that the system might not be forwarding emails to Mailjet, as there’s no indication of any email attempt in Mailjet's logs, despite verified domains and following the configuration documentation exactly. Additionally, the only logs available in the app (hosted on Heroku) are web requests for the web interface—no email-sending activity appears in the logs.
( PS: This my first time posting an issue on github, if you need any more info to help me out please ask :) )