Information
Email system availability depends in part on best practice strategies for setting tuning configurations. This configuration controls the maximum number of simultaneous outbound connections from a domain and works in conjunction with the Maximum Outbound Connections Count setting as a delivery tuning mechanism. If the limit is too low, connections may be dropped. If the limit is too high, some domains may use a disproportionate resource share, denying access to other domains. Appropriate tuning reduces the risk of data delay or loss.
By default, a limit of 20 simultaneous outbound connections from a domain should be sufficient. The value may be adjusted if justified by local site conditions.
Solution
Update the EDSP.
Open the Exchange Management Shell and enter the following command:
Set-TransportService -Identity <'IdentityName'> -MaxPerDomainOutboundConnections 20
Note: The <IdentityName> value must be in quotes.
or
The value as identified by the EDSP that has obtained a signoff with risk acceptance.