can you help me find out why this outgoing email was quarantined?

This is the delivery log:

[2020.12.10] 10:51:21.667 [7011306] Delivery started for info@tibteatro.it at 10:51:21
[2020.12.10] 10:51:42.717 [7011306] Added to SpamCheckQueue (1 queued; 0/30 processing)
[2020.12.10] 10:51:42.717 [7011306] [SpamCheckQueue] Begin Processing.
[2020.12.10] 10:51:42.717 [7011306] Blocked Sender Checks started.
[2020.12.10] 10:51:42.888 [Cyren Client] Start Scanning Message. Enabled Services: All, MailFrom: info@tibteatro.it, SenderIP: 79.54.240.201, MessagePath: s:\SmarterMail\Spool\SubSpool6\7011306.eml10:51:42.998 [Cyren Client] Done Scanning Message. MessagePath: s:\SmarterMail\Spool\SubSpool6\7011306.eml Results AV: Unknown, AS: Unknown10:51:42.998 [7011306] Spam Checks started.
[2020.12.10] 10:51:42.998 [7011306] Spam Checks skipped: User authenticated
[2020.12.10] 10:51:42.998 [7011306] Spam Checks completed.
[2020.12.10] 10:51:42.998 [7011306] Removed from SpamCheckQueue (0 queued or processing)
[2020.12.10] 10:51:45.732 [7011306] Added to RemoteDeliveryQueue (1 queued; 0/50 processing)
[2020.12.10] 10:51:45.732 [7011306] [RemoteDeliveryQueue] Begin Processing.
[2020.12.10] 10:51:45.732 [7011306] Sending remote mail for info@tibteatro.it
[2020.12.10] 10:51:45.732 [7011306] Message flagged for Quarantine
[2020.12.10] 10:51:45.732 [7011306] This message cannot be delivered as it was marked as spam. Weight: 0
[2020.12.10] 10:51:45.732 [7011306] Delivery for info@tibteatro.it to info.theo.longuemare@gmail.com has bounced. Reason: This message cannot be delivered as it was marked as spam.
[2020.12.10] 10:51:45.732 [7011306] DSN email written to 7011311 with status failed to info.theo.longuemare@gmail.com
[2020.12.10] 10:51:45.732 [7011306] Process delivery status notification step from recipient success. Recipient: [info.theo.longuemare@gmail.com], Notify: [], LastError: [550 This message cannot be delivered as it was marked as spam.], RanDomainFilter: [False], RanGlobalFilter: False
[2020.12.10] 10:51:45.732 [7011306] Delivery for info@tibteatro.it to info.theo.longuemare@gmail.com has completed (Bounced)
[2020.12.10] 10:51:45.732 [7011306] Removed from RemoteDeliveryQueue (0 queued or processing)
[2020.12.10] 10:51:45.842 [Cyren Client] Start Scanning Message. Enabled Services: All, MailFrom: paghe14@studioscudeller.it, SenderIP: 151.69.122.122, MessagePath: s:\SmarterMail\Spool\SubSpool0\7011310.eml10:51:45.857 [Cyren Client] Start Scanning Message. Enabled Services: All, MailFrom: michela@revert.it, SenderIP: 82.184.89.54, MessagePath: s:\SmarterMail\Spool\SubSpool9\7011309.eml10:51:45.904 [Cyren Client] Done Scanning Message. MessagePath: s:\SmarterMail\Spool\SubSpool9\7011309.eml Results AV: Unknown, AS: Unknown10:51:48.748 [7011306] Removing Spool message: Killed: False, Failed: False, Finished: True
[2020.12.10] 10:51:48.748 [7011306] Delivery finished for info@tibteatro.it at 10:51:48    [id:7011306]