Winmail.dat Attachment Exchange

When external recipients complain about receiving attachments in winmail.dat format ( or sometimes  ATTxxxxx) this is most likely caused by the formatting. To be more concrete it is caused when Exchange uses RTF ( RichTextFormat ) for sending mails to external recipients.

To solve the winmail.dat issue on serverside the external recipients should be added as Mail-Contacts to the Exchange organization. You can force Exchange to never use RichTextFormat when sending mails to these Mail-Contacts. 

To force Exchange to never use RTF format when sending to external contacts use :

Exchange 2010 Multi-Tenant : ( for a certain Mail-Contact ) 

Get-MailContact -Organization “TenantName” -Identity “Mail-ContactName” | set-mailcontact -usemapirichtextformat never

Exchange 2010 Multi-Tenant : ( for all Mail-Contacts in an organization )

Get-MailContact -Organization “TenantName”  | set-mailcontact -usemapirichtextformat never

Exchange 2013 / 2016 Multi-Tenant : ( for a certain Mail-Contact )

Get-MailContact -OrganizationalUnit “TenantName” -Identity “Mail-ContactName” | set-mailcontact -usemapirichtextformat never

Exchange 2013 / 2016 Multi-Tenant : ( for all Mail-Contacts in an organization )

Get-MailContact -OrganizationalUnit “TenantName”  | set-mailcontact -usemapirichtextformat never

For Exchange OnPremise you should most likely use these CMDlets without the -Organization or -OrganizationalUnit switch.

You can also consider to use the Remote Domain solution.

Since we only have Multi-Tenant environments we want to control this on organization level. For this reason we did not mess with the Remote Domain.  Hence we have not tested it. But a comment on this from someone , who has implemented the Remote Domain solution in a Multi-Tenant environment , would be well appreciated.

This will solve the problem on serverside. Attachments will not longer appear as winmail.dat files.

See a client side solution here :

Winmail.dat Attachment Outlook

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