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Q: How can I use LISTSERV with the Exchange Online cloud service?

Many of our Windows customers are migrating their office software to third-party cloud vendors like Microsoft's Office 365 or Google Apps. When they do this, their local Exchange server also migrates to the Exchange Online cloud, and there is no longer a local mail server that can be used by LISTSERV for sending out email. This tech tip looks at how to authenticate your outgoing email so that it's accepted by Exchange Online.

One solution is to install the Microsoft SMTPSVC mailer on the LISTSERV machine and use that to mail directly to recipients. We already offer a white paper that explains how to do this: Using the Microsoft IIS SMTP Service for LISTSERV Deliveries.

However, this still requires local expertise to set up and maintain the local SMTP server as well as manage ongoing delivery issues. Other customers want to have the LISTSERV mail routed through their Exchange Online server in the cloud and let Microsoft manage the mailer and any deliverability issues for them. The problem with this is that Microsoft cannot and will not accept incoming email for onward forwarding unless the source of the email is authenticated as coming from a known, authorized source.

The problem is further complicated in that LISTSERV itself cannot perform the necessary SMTP authentication. The solution is to use the Microsoft SMTPSVC mailer on the LISTSERV machine in a slightly different manner than described above and let SMTPSVC do the necessary authentication so that the email will be accepted by the Exchange Online server and forwarded on to wherever it needs to go. This tech tip details the changes and additions necessary in the SMTPSVC configuration to make this possible.

Briefly, the steps needed are to configure a "smart host" (the mail server in the Microsoft cloud). You may also need to change the port number from 25 to something like 587. Lastly, you will need to configure a user ID and password. You will get all of these details from your Office 365 support staff.

First of all, open the IIS6 Manager. This is the only interface that Microsoft provides to administer SMTPSVC, even in Windows 2012. Click on the "Delivery" tab, then the "Advanced" button. Enter the name of the "smart host" server and click OK. By defining a smart host, you are telling SMTPSVC to send all outgoing mail to this other server and to not perform the usual DNS lookup and attempt to send directly to various destinations.

Next, click on the "Outbound Connections" button to configure the TCP Port (if different from the usual port 25).

Finally, click on the "Outbound Security" button to enter the user ID and password as provided by the Office 365 vendor.

At this point you are ready to test the connection. If all is well, everything will work as intended and mail will be forwarded from LISTSERV to the cloud mail server and then onward to wherever it needs to go.

For more information see this Microsoft article:

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