Messenger not working if use more users at a same time

Dear Support Team,

Messenger not working when teachers send to mail students at a same time.

Hmm, this is unusual, as it should be able to send as many messages as needed. Can you let us know the steps to reproduce the issue you’re seeing? Be sure to also check your View Logs in System Admin for any “Email send status” and “Background process” logs that may indicate an error in sending messages, as well as check your System Settings and let us know if background processing is on or off. Are you using SMTP mail, and could there be a rate limit on the message sending from whatever mail server you’re using. Every system works differently, so the more information you’re able to share to help troubleshoot, the better.

Test Case-1:
If single user (teacher) using messenger, email sent successfully.

Test Case-2:
If multiple users (teachers) using messenger together for sending email, email delivery failure happens.

Please review the below supporting information in this post and do the needful:

  1. please find attachment for system log - Background process

  2. System log - Email send status

  3. We are using SMTP mail, please find SMTP Mail Setting below

  4. Background process is “Yes”

  5. Sender email is GSuite account with Subscription “Education Standard”

This is odd, it looks like code 421 from GSMTP refers to the following error “421, “4.7. 0”, Our system has detected an unusual rate of unsolicited mail originating from your IP address.” This suggests the limit is on Gmail’s end, rather than Gibbon. Have you checked that you have setup the SMTP relay authentication settings in your Google Admin account, such as “Only accept mail from the specified IP addresses” along with the IP address of your server. I believe if you don’t have strict authentication settings, then Gmail will limit the amount of mail you can send, to prevent using its servers for sending spam. Be sure to check the settings: