Hi,
The screenshots you post includes personal information, like domain name/IP address, please cover those information.
It seems you don't have PTR record for the IP address that mail.contoso.com pointing to, can you try adding a PTR record in your DNS Zone? Create a DNS PTR record
Also, the fqdn of your send connector misses "." in the fqdn, please correct it with Set-sendconnector(or create a new one, fqdn is blank by default):
Set-SendConnector "name" -fqdn mail.contoso.com
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