Configuration in Exchange Online on Office 365 Portal

  • Create a rule to disable built-in spam filtering when emails are received from your IP address using following steps:

IP Throttling on Exchange Online

When using Xeams in the front, servers on Office 365 will see every message coming from your IP address, which could kick in the rate limits on Microsoft's end and you could see the following error message in the SMTPOutboundConversation.log.

451 5.7.(500-699) Server Busy. Please try again later.

The following steps are copied from this page on Microsoft's site to add a connector, which resolves this issue.

  • Log in to Exchange portal on
  • Click mail flow
  • Click connectors
  • Click the icon to add a new connector.
  • Select Partner organization for the From and Office 356 for To, similar to the image below. Screen shot...
  • Provide a name for this connection on the following screen.
  • Select Use the sender's IP address on the following screen. Screen shot...
  • Add the IP address where Xeams is running on the following screen.
  • Next, leave Reject email messages if they aren't sent over TLS. Screen shot...
  • Finally, save the settings