Can't send an external mail to specific recipient.

Error "554 5.7.1 <sender address>: Relay access denied" returns from the recipient server and mail can't be delivered.

1. Recipient server blocks Symantec.cloud IP range at their side.
2. There are some policies created by recipient server to block the connection of Symantec.cloud.
 

Contact the administrator of recipient server to remove the block of Symantec.cloud.