The organisation I work for has a VPS on which several services run in Docker containers, on top of which, another Docker container runs a Traefik reverse proxy to do what reverse proxies do.Last Monday, late in the morning, all the containerised services running on that server started to fail to send SMTP request to our mail server (which is hosted on another dedicated server). That other server works fine, and we can still send emails through it using other mail clients like Thunderbird, Mailspring, or the Modoboa web client running on the same dedicated server etc... But the web client Roundcube (PHP based) hosted on the VPS fails to send emails. Another service failing to send emails is a Weblate (Django based) service showing this error message:
weblate.E003 Cannot send e-mail ([Errno 111] Connection refused), please check EMAIL_* settings.I know the problem does not come from the configuration of those services, which ran uninterrupted since before the problem occurred. Nobody I am aware of touched anything in the server when the bug appeared, its IP address is not blacklisted by the mail server. I tried in vain to grasp where the problem could emanate from ever since.The rest of the services run normally, we still receive emails on Roundcube, the other web apps are served properly.
I am open to any suggestion really, and will keep editing the question based on your feedbacks. Thanks in advance.