Emails not queued and ignored when sending limit reached

Description:

Emails server setup using Authenticated SMTPS to localhost email server on port 465

The email server limits connections to 5 per IP as a security device.

If Rocket sends say 40 email notifications this overloads the server but Rocket does nothing - doesn't queue the mails or send an error.

It just seems to fire and forget.

Steps to reproduce:

Setup Email server with authenticated login on port 465
Set Max Connections per IP to 5
Ping @all or similar

Expected behavior:

All mails should be sent - those that the sender rejects should be queued and resent
Unsent mails should throw an error.

Actual behavior:

Notification emails get limited to 5 and the rest rejected and never sent.
Rocket gives no information on this.

Server Setup Information:

• Version of Rocket.Chat Server: 6.6.7
• Operating System: Linux
• Deployment Method: docker (rocket only, not mongo)
• Number of Running Instances: 1
• DB Replicaset Oplog: replicaset enabled, oplog disabled
• NodeJS Version: 14.21.3
• MongoDB Version: 5.0.26-1

Mail server log can be supplied on request.

Start by tracing Rocket.Chat's notification email sending path and how authenticated SMTPS connection-limit rejections are handled. Reproduce the issue with a five-connection-per-IP mail server and inspect the available server logs. Done means rejected messages are retried or queued, and permanently unsent messages produce an error or other clear notification.