Increase the number of queue runners that are configured in Proofpoint that's appropriate to maintain the same message throughput before and after you change the number of messages per connection.Start at this value and reduce it if ConnectionReset errors are still logged. Proofpoint recommends an initial value of 199. Set the value of Maximum Number of Messages per SMTP Connection to a number that's based on the average message size and average network throughput to Exchange Online.To avoid this situation, do the following: This entry prevents Proofpoint from retrying the message immediately. These errors cause Proofpoint to identify Exchange Online as a bad host by logging an entry in the HostStatus file. If the number of messages that are sent by Proofpoint is more than the number that can be transferred to Exchange Online within this time frame, mail delays occur and ConnectionReset error entries appear in the Proofpoint log. However, Exchange Online maintains each connection for only 20 minutes. Specify a limit for the number of messages per connectionīy default, Proofpoint does not limit the number of messages that it sends per connection. Make the following changes to the Proofpoint default settings.

Affected tenant admins have confirmed that these changes resolved their mail delay issue without introducing other issues. To prevent these delays, Microsoft and Proofpoint Support and Operations teams have identified changes that must be made to the Proofpoint settings for both cloud and on-premises deployments. This situation causes long mail delays of an hour or more. In this configuration, if Proofpoint encounters a deferral from Exchange Online, its default settings prevent it for a long time from retrying the email messages. It involves connecting Proofpoint and Exchange Online so that Proofpoint provides the first level of email filtering and then sends email messages to Exchange Online. Exchange Online supports integration with third-party Sendmail-based filtering solutions such as Proofpoint Email Protection (both the cloud service and on-premises deployments).Ī popular configuration is shown in the following figure.

Setup microsoft exchange server 365