Exchange Server Troubleshooting: Winmail.dat issue while migrating from Domino

Introduction

This article sheds light on the winmail.dat issue throughout the process of Migration from Notes to Exchange or Office365!

Stages where the issue occurs

• During the testing and provisioning stage: In the process of initially signing the tenant you start working to test with the coexistence setup, all email which contains Microsoft Office documents as attachments will be delivered to Lotusnotes as "winmail.dat"
• During the post production stage: After resolving the first occurrence of the issue initially at the stage of testing, now a few people will be experiencing the same issue as earlier.  But now only few users, all other users will be able to receive the Microsoft Office documents as expected.

Cause

In the first occurrence the Exchange is using TNEFE format by default, or Transport Neutral Encapsulation Formatting. If the message is sent using TNEF and the recipients’ email client does not understand or intercept TNEF, the message can’t be ‘decoded’ and all that arrives is a binary WINMAIL.DAT file.

There are many posts online discussing this problem being related to Outlook and the Rich Text, but in this case, no matter which format you select in Outlook (RichText, HTML, and PlainText) the attachments will be delivered as winmail.dat.

In the second occurrence, this may be unique to migrations using Dell Coexistence Manager.  However it can be experienced in other scenarios also while using “MailContacts” to route the email. 

When a Mail Contact has the routing address set as primarysmtpaddress, this issue occurs, for example:

User1 is in notes and his address is user1@consto.com and user2 is migrated to exchange and his address is user2@consto.com .  For a simple coexistence to work every exchange should be configured with a routing address in a mail connector.  For this scenario let is assume that the routing domain name is notes.consto.com.

When the user2@consto.com wants to send an email to user1@consto.com exchange must have a primarysmtpaddress  user1@consto.com and targetaddress attribute should be smtp:user1@notes.consto.com which will deliver the email from exchange user to Notes user through the exchange mail connector.

But when the user1 has primarysmtpaddress as  user1@notes.consto.com notes user will experience the winmail.dat issue even though the mailflow is not affected.

With respect to Dell Coexistance Manager, this issue occurs when you run the groups provisioning wizard before the completely running the directory connector.

Resolution      

For the first occurrence, run the following command on the tenant through PowerShell  user account with global admin privileges.

Set-RemoteDomain Default -TNEFEnabled $false

Set-RemoteDomain routingdomain -TNEFEnabled $false

Note: routingdomain is the domain you have configured in the exchange mail-connector.

For the second occurrence, delete the mail contacts with this particular issue and then run the Directory connector from Dell Coexistence Manager.  After the completion of the Directory Connector cycle, run the Groups Synchronization wizard.