TNEF Issue - Winmail.dat or messages stuck in submission queue

Question

Hi guys, 
I've looked around the forums and have found people that have had submission queue issues when they set TNEF to $null or $false, and have found that the unified answer is to set TNEF to $true.
I also see folks having issues with recipients in remote domains receiving winmail.dat files in some instances (with a .pdf or .xls file attached) if TNEF is set to $true.
I have both issues. If I set TNEF to $true, I encounter the winmail.dat file problem. If I set TNEF to $false or $null, I encounter the submission queue issue (submission queue states "A transient storage failure occured", and users get a queue
expiration bounce). Neither of these states are acceptable. I cannot have messages stuck in the queue only to be expired, and I cannot have recipients in remote domains failing to receive attachments in emails. 
Does anyone have a possible workaround that might resolve this particular situation? It seems that this has been an issue in Exch 2010.
Current Environment Configuration:
I am running Exchange 2013 SP1 Standard on both of my CAS/MBX servers, running on Server 2012 R2 patched to the latest updates. I have an inbound spam filter, but mail outbound is not filtered, therefore the spam filter on our side should not play a role.
I do have not made any changes to the exchange default malware filter either. Other than this issue, mail is flowing correctly and as expected.

Answer 1

I also see folks having issues with recipients in remote domains receiving winmail.dat files in some instances (with a .pdf or .xls file attached) if TNEF is set to $true.
Hi,
According to your description, my understanding is that all the remote domain's recipients would receive winmail.dat files when you send the message to them if TNEF is set to $true, right?
The Winmail.dat file is used to preserve Rich Text formatting. Outlook uses it when sending a Rich Text-formatted message. During transport, the content of the message may be changed, preventing the receiving client from being able to read the formatting
instructions. In other cases, the receiving client does not use or recognize the winmail.dat file.
I recommend that you refer to the following article to solve the issue:
http://support.microsoft.com/kb/278061
Method 1: Change the default message format
The sender can change the format of the email messages that they send by using the following steps:  
On the Tools menu, click Options, and then click
Mail Format.
In Compose in this message format, click to select Plain Text, and then click
OK.
NOTE: To send to certain recipients that use RTF format and others recipients that use plain text format, the sender must set the option for the recipient in either the Personal Address Book or the recipient's contact record.
Method 2: Modify the recipient's entry in the Personal Address Book
The sender can use the following steps to remove the RTF format from the recipient attribute in the Personal Address Book:  
On the Tools menu, click Address Book.
In Show Names From, click the Personal Address Book.
Select the addressee that you want to set as plain text, and then click
Properties on the File menu.
In the SMTP-General tab, click to clear the Always send to this recipient in Microsoft Exchange rich text format check box, and then click
OK.
Method 3: Change the specific contact format
The sender can use the following steps to set plain text in the recipient's contact record:  
Open the recipient's record in the Contacts folder.
Double-click the recipient's e-mail address.
In the E-Mail Properties dialog box, click Send Plain Text only under
Internet Format.
Method 4: Set the Outlook Rich Text Format Internet e-mail setting
In Outlook 2003 and Outlook 2007, click Options on the Tools menu.
Click the Mail Format tab.
Click Internet Format.
Under Outlook Rich Text options, click either Convert to HTML format or
Convert to Plain Text format.
Hope this helps!
Thanks.
Niko Cheng
TechNet Community Support
Niko,
The Winmail.dat issue is only part of the problem, as described in my original post. For these messages (which it's a different set of messages every time, and it's becoming impossible for me to track them all down), if I set exchange or outlook to encode
the message in Rich Text, the message gets encoded and sent to the recipient. Some of our recipients will reject the message because it is rich text, others receive a winmail.dat file.
However, if I set exchange to not encode messages (TNEF= $false or $null), the message becomes stuck in the submission queue and eventually times out with an error resembling "Storage Transient Failure".