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Preventing Winmail.dat problems since upgrading to MAPI-enabled SmarterMail
Problem reported by Douglas Foster - 1/19/2021 at 11:29 AM
Not A Problem
Perhaps we are unusual, but we have some legacy domains in Exchange from corporate acquisitions, as well as SmarterMail for our primary user base.    Since upgrading to MAPI-enabled SmarterMail, we have been having problems with some messages from Exchange domains arriving into SmarterMail with Winmail.Dat attachments.   Some web articles leave the impression that this will only happen if the user message is prepared in RTF format, but this is not correct.   Our problems occurred on HTML-formatted messages with attachments.   One web article said, apparently correctly, that TNEF contains supplemental content which only Outlook understands, and it can be attached to base messages with any format.

I remember reading, a long time ago, that the actual processing depends on Exchange believing that the target system is another Exchange server, as well as the message formats.  So apparently SmarterMail now successfully mimics an Exchange server.

Another web search provided the global solution.    In Exchange Management Console, navigate to Organizational Configuration...  Hub Transport... Remote Domains.   Open the properties window for Default or another object.   From the Message Format tab, change "Exchange rich-text format" to "Never use"

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Luk Replied
From my own experience (we have exchange/smartermail mix) winmail.dat issues are usually related to autocomplete feature in Outlook. Clearing autocomplete Cache in Outlook resolves this issue for us.
Not sure if it will hepls you but worth to try.
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Douglas Foster Replied
Just to verify, you are recommending this option for the sending users:
File... Options... Mail... [Empty Auto-Complete List]
(or disabling the feature by clearing the related checkbox).

Is this correct?
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Larry Duran Replied
Employee Post
Hey Douglas are you having an issue seeing the files contained within a winmail.dat attachment or is it that you're having an issue properly seeing RTF formatted emails?  The winmail.dat attachment issue is something that we recently fixed in MAPI and should be in our latest public release.
Larry Duran
Software Developer
SmarterTools Inc.
(877) 357-6278
www.smartertools.com
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Luk Replied
Yes, just Empty Auto-Complete List for sending user.
 If userA (exchange) is sending email to userB (Smartermail) and userB gets winmail.dat attachment, clearing Outlook Auto-Complete List on userA Outlook fix this problem in our environment but we are using Smartermail 15 and Exchange 2019.
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Tim Uzzanti Replied
Employee Post
Winmail.dat is very client dependent.  For example, Mac Mail and Outlook for Mac both handle Winmail.dat very differently even though they both use the same protocol (EWS).

The more recent versions of SmarterMail accommodate various clients very differently so that there is a much higher chance that Winmail.dat can be properly processed by a specific client.  In SmarterMail 15, we basically leave Winmail.dat alone and rely solely on the clients and results with vary much more.

How auto-complete would affect this is not clear to us.

Winmail.dat is an abomination and no matter what servers or clients you use you will see them from time to time but with the most recent versions of SmarterMail, we do a really good job minimizing the frequency in which they are seen.

Hope this helps,
Tim Uzzanti
CEO
SmarterTools Inc.
(877) 357-6278
www.smartertools.com
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Luk Replied

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