Make sure the TLS is enabled on the connector that you used to relay emails. Make sure the device that you used supported TLS and use the same version as Exchange server.
About the SSL, I would suggest you use command below to check whether the connector is configured correct:
Send-MailMessage -SmtpServer mail.domain.com -Credential $credential -From 'user1@domain.com' -To 'user2@domain.com' -Subject 'Test email' -Port 587 -UseSsl
If you could send from the command successfully, if means this issue may related with the tool that you used.
If you cannot send email from this command successfully, it mean there exist issue with the connector that you used, you could follow this article to check the configuration on your connector.
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