Hello, Thank you in advance for your time and consideration to this situation.
Two separate business entities, with their own contracts and ESAs, are unable to mail 2 seperate on-prem exchange business entities.
Sender1 cannot send to Receiver1
Sender2 cannot sent to Receiver2
Both are on-prem exchange 2013, are not blacklisted, and the emails are not reaching their servers.
Just so happens we manage the IT for both of these Receivers. The two Senders have their own IT and contracts with Cisco. They are ADAMENT its not them. But I have yet to talk to their IT team.
After disabling all antispam, and transport agents on the two exchange servers, running a mail trace, sending a simple test email to the Senders 1 and 2 (from Receiver 1 and 2 respectively) the Senders claim to have replied to that email, but nothing touched the server per mail-trace and deliverability logs.
I am here asking anyone with experience in Ironport outgoing email filtering, what specific settings or whitelists I need to request the Sender's IT to perform.
Thank you again for any information you may be able to provide.
