Hi @Syed Afsar ,
i am using exchange server 2019 on premises when we send messages to outlook domain we are getting the above message
By "Outlook domain", do you mean outlook.com or hotmail.com accounts? If this is the case, based on my research, it's recommended to read this FAQ first and the delisting form for Outlook.com, the consumer service can be found via this link: https://support.microsoft.com/supportrequestform/8ad563e3-288e-2a61-8122-3ba03d6b8d75.
If you also have the issue sending mails to recipients whose email address are in Microsoft 365, you can use the delist portal (https://sender.office.com/) to remove yourself from the blocked senders list.
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