Fortisandbox quarantine

Hello friends, I have a problem: users tell me that an email with attachments does not arrive. i check the logs in the fortimail and effectively it is visualized that they were quarantined "system quarantine; defer disposition" I had to enter the fortimail and release them from quarantine after 4 hours they were in queue.

The weird thing is that a user did receive the email immediately after it was sent. check the logs again and you see the following: (image 1)

but for the other users who did not receive the mail, the following log is displayed: (image 2)

because for the other users the mail did not reach them and why to a user if the mail arrived fast?