Emails Passing but sending a bounceback message

[bennhana]

Hi all

I don't know if anyone has ever come across this issue. I have a client running a Zimbra mail server and a few users on the LAN when they send emails the recipient is getting them but the sender gets a bounceback message like shown below.

Your message did not reach some or all of the intended recipients.

Subject:

Sent: 23/02/2023 07:24

The following recipient(s) cannot be reached:

<user> on 23/02/2023 07:25

None of your email accounts could send to this recipient.

If anyone knows this problem and has a solution please, help.