STATUS: FIXED This was fixed in build 16.0.8229.2073. To install the fix, go to File > Office Account > Update Options > Update Now.
Some users are discovering that Outlook sends winmail.dat files attached to messages when sending to contacts in their address book. Only Outlook on Windows desktop (all versions) is affected; messages sent from Outlook on the web or the Outlook app do not have the rogue winmail.dat file.
The problem: When sending email to any contacts from your address book in Outlook, some recipients receive a winmail.dat file attachment that shows up in some clients. Outlook should decode the winmail.dat file and correctly display any attachments, however, if not, the attachment icon may be displayed but no attachment is shown.
Gmail & Yahoo web mail should decode the winmail.dat file and show the attachment but HTML formatting will be lost. The Internet header will mention the winmail.dat file:
--_000_CY4PR12MB1750DB40ADDCB9EF8B1C7E1FCC5D0CY4PR12MB1750namp_
Content-Disposition: attachment; filename="winmail.dat"
Content-Transfer-Encoding: base64
Content-Type: application/ms-tnef; name="winmail.dat"
The keywords are "address book". If you select a contact and click the Email command on the ribbon or right-click and choose Create > Email from the context menu the message does not have the winmail.dat attachment.
As has always been the case, the winmail.dat file is more of a confusing nuisance than anything. The recipients receive an attachment and don't know what to do with it. (Correct answer: ignore it.) Note: Gmail and Yahoo recipients will lose HTML formatting but attachments will be accessible.
The usual fixes (listed at Outlook is Sending Winmail.dat Attachments) don't seem to work for most people or are only temporary and the problem returns. This is likely because the address book is the problem, not the contacts specifically.
It appears that this bug has reappeared. Have you gotten any other reports? I'm on Monthly Channel (Targeted), with the most current update.
No, you are the first. I'll see if i can repro with my account.
Still having the same issue as well. Running updated Outlook 2016 against Outlook.com.
Do you know what build you have? You should have the updates if you have a subscription but may not if you have a retail perpetual version.
This here seems to help (sorry is translate from german with other named menupoints):
- Outlook
--- Options
---- Advanced
-----> Coding for outgoing messages: Change to "Unicode UTF-8"
The standard is (in germany) "Westeuropäisch (ISO)", that have sometimes problems.
Thanks for this, Matthias. As of today I still have this winmail.dat problem when sending atttachments from my Outlook account to 3rd parties.
I have noticed that recipients are okay if they're reading the email from Outlook on a PC. If they're using an IOS device, the same email shows the winmail.dat error and the attachment can't be viewed.
I tried your suggestion of changing the coding for outgoing messages to UTF-8 (from Western European ISO).
It worked.I spoke to soon. This isn't fixed. Please ignore my previous message.
>>> I have noticed that recipients are okay if they're reading the email from Outlook on a PC. If they're using an IOS device, the same email shows the winmail.dat error and the attachment can't be viewed.
Outlook is the only client that can decode the winmail.dat, although gmail and possibly yahoo now decodes them, although I'm not sure if it's only when reading in a browser.
I thought this was fixed in a recent update but have been on vacation and not watching all updates that came out, so i could be wrong (and mixing it up with other outlook.com bugs that were fixed.)
Here is a weirdness that I discovered in my Outlook 2016 address book. You might want to report it to Microsoft since it could be related to the winmail.dat problem. My contacts have Name (John Smith), Company (Contoso) and email address (JSmith@Contoso.com). Previously the "Display As" field was configured as "John Smith (JSmith@Contoso.com)". Recently some update to Outlook changed "Display As" on *all* my contacts to just "JSmith@Contoso.com". If I call up the contact, blank the "Display As" field and hit TAB, the "Display As" field is changed to "John Smith - Contoso (JSmith@Contoso.com)". Note the "dash company" that is inserted. If I save the contact, call the contact back up, blank the "Display As" field and hit TAB again, this time the "Display As" field is changed to "John Smith (JSmith@Contoso.com)". It is exceedingly weird that it takes two updates/saves to change the "Display As" field back to its original format. I did run a test, and changing the "Display As" field back to its original format did not fix the winmail.dat problem. (I didn't clear the auto-complete cache or stop/start Outlook, however.) Hopefully Microsoft already has fix(es) for the winmail.dat issue and this issue. If so, do you… Read more »
>> If I call up the contact, blank the "Display As" field and hit TAB, the "Display As" field is changed to "John Smith - Contoso (JSmith@Contoso.com)". Note the "dash company" that is inserted.
Are you using more than one computer? If you edit the contact on a second computer, it shows up with the company name on the other computers. Editing it fixes it on that computer, but the company name version syncs to the others... it goes round and round. I hadn't noticed it blanking out though. Will see if i can repro.
At this time, i don't have any additional information on the status of a fix.
Just using one computer. (Lenovo ThinkPad T440s, Win10 Pro)
Syncing with a smart phone or editing contacts in outlook on the web?
Outlook 2016Outlook.comOutlook (Android)Android Contacts. All editing is done in Outlook 2016. (Contacts can't be edited in Outlook (Android), of course. Grumble, grumble.)
I also get a whole bunch of weird errors if I run Microsoft OffCAT against Outlook 2016. I can send you a screenshot if you like.
yeah, please on the screenshot. offcat should be erroring.
Where is the upload link? (Or am I staring at it?)
The Commenting System mangled my sync'ed chain of address books/contacts. Key point was that all editing is done in Outlook 2016, with everything passing through Outlook.com to various Android devices.
Where is the upload link? (Or am I staring at it?)
FYI - I am not getting notifications of replies, possibly because the Commenting System can't handle my unusual e-mail address.
You might be staring at it - or it's not visible due to caching or something out of your control.
It's just to the bottom right of this text field. If you don't see it, try using a different browser.
Got it. Unfortunately I can't upload a PDF or an .offx (OffCAT export) file. Can you PM another method/address?
I temporarily turned PDF support on - i don't normally allow anything but images for security reasons.
Sending the PDF. Unable to send the .offx. OK to pull up the drawbridge.
Still no notifications.
There are a lot of confirmations being sent - actually, it looks like maybe you are subscribing to a specific comment (but I could be misreading it). There were 9 confirmations and only one accepted - i accepted the others - so if you get 9 copies of replies, that is why. It's sent via exchange server - i ran a message trace and the confirmations were all delivered but no actual comments (that is why i think it is for a specific comment). Will check the trace on this...
Could be operator error. I subscribed on the initial post, but each reply also has a "Notify of new replies to the comment" checkbox. I'm a belt and suspenders kind of technoid, so I've been checking that box and confirming the subscription after each reply. I won't do it for this reply to see what happens.
I did receive your test message.
Anything useful in the barrage of OffCAT errors? Any update from Microsoft about them fixing this anal trauma (and undoing the damage to the "Display As" field)? Patch Tuesday is only a week away.
They have not said how soon, so my money is not this week. i will check it in the next insider build (usually out on Thurs/Fri) - they are usually about 4 weeks ahead of general availability.
I just noticed that Microsoft also screwed up the "File As" field in all my contacts. It was changed from "Smith, John (Contoso)" to "Smith, John(Contoso)"....with no space between John and the open parentheses. As a result, the name and company appear run together on one line in the Contacts instead of on two lines.
If you do have a communication channel with Microsoft, you might suggest that they do some research on such interesting topics as "Quality Assurance" and "Regression Testing."
I hadn't noticed that - will let them know. Thanks.
Any update on the progress of Microsoft's rectal encephalectomy? I'm getting really tired of having to remember to flip over to Outlook.com if I need to send an attachment.
i haven't heard - will check the latest insider build to see if it fixed it. (Sending from the contact should work correctly.)
Something else appears to be broken. I received a marketing e-mail from a local nursery with lots of pretty pictures and forwarded it to my wife from Outlook 2016. All she got was links. When I forwarded the same e-mail from Outlook.com it was fine. I confirmed this with a different forwarded e-mail with embedded pictures. The links to the pictures in the nursery marketing e-mail were to sendgrid.net. The links in the second test e-mail were to mailchimp.com.
Something else for Microsoft to fix .........maybe .......hopefully ........someday.
did she get a plain text copy? If so, that is "normal" when there is a winmail.dat file.
Yes she did. I didn't realize that this new Microsoft feature would kill embedded links as well as attachments.
it's not a new feature, it's a bug, but that is a side effect of seeing the winmail.dat file.
i don't think the smtp server is blocking .name extensions, but i will double check on it.
There are a lot of errors in the offcat - i would definitely disable the norton plugin. not sure if it is causing all of your problems, but it is not needed and can cause problems.
Some of these errors may be unique to outlook.com (due to features turned off for consumer accounts), but it also says you are delivering exchange mail to a pst - you should be using the mailbox cache.
If autoaccount setup doesn't work, you need to delete a value from the registry...
The weirdness continues. I re-ran OffCAT, and along with the usual pile of errors it reported that Outlook 2016 was down-rev. I updated to Build 16.0.7870.2024, and then ran OffCAT again. It only reported one error, involving hyperlinks. Success! But with 45 years of IT scar tissue, I ran OffCAT again and the 23 errors were back.
The upgrade didn't fix the attachment issue.
I have one Outlook.com account linked to an .OST file, an Office 365 account also linked to an .OST file, an Archive.PST file and three .PST files with nothing but contacts in them and no e-mail links. In the OffCAT Configuration Details for the Office 365 account I can see the error about a .PST file being the default, but that is one line below where the .OST file is displayed. Account Settings for both the Outlook.com and Office 365 accounts show that mailbox cache is being used. Any idea what is bent, or suggestions on how to fix? Should I blow away and rebuild (once again) the Office 365 .OST file?
i would try a separate profile with just one of the accounts in it - run offcat on it and see what comes up. Definitely sounds like offcat is screwy, but I don't know if it's due to the accounts in the profile or if its just screwy.
I did disable the Norton Anti-Spam plugin, both in Outlook 2016 and Norton.
Microsoft's changeover to the Exchange platform for Outlook.com has been a total screw-up. They forced everybody to rebuild their .OST files, but it was impossible to do the rebuild with Two-Factor Authentication turned on. I had to disable 2FA, and I haven't been brave enough to turn it back on. I'm afraid it would break Outlook/Outlook.com again.
if you use 2-factor, you need to use the app password in outlook. At this time, Outlook won't pop up the second screen.
I can't remember the details, but the app password wouldn't work either. I ended up having to disable 2FA.
One more bit of information. I also have several .PST files with only contacts in them. The "Display As" field in those files was not changed.
Yes, only outlook.com account should be affected by this bug.
Thank you for the article. This has become a nightmare trying to figure out how to fix this. My boss is the only one who gets these wind dat files and he is getting very upset about it. I do not want to work out of Outlook.com all the time as I do not care for it.
I cannot seem to fix mine and was wondering if you could help me in further detail.
Microsoft is investigating it but I don't have an ETA for a fix. For new messages, don't use the To button or autocomplete - go into contacts, select his contact then click EMail button in ribbon. If the problem occurs on replies, try creating the new message from contacts then copy the address and paste into the To field of the reply.
Diane
Any more news about this bug being fixed. Your work-arounds have been a life saver but having to use the email button or sending the whole message as plain text is a real pain. I use Outlook 2010 and 2016 with an Outlook.com email address and if this is not resolved I think I will need to move to Gmail.
John
It's supposed to be fixed in 16.0.8229.2073. insider builds are into 83xx so if that's not the current build, it will be released very soon.
Thanks Diane that is good news.
I am still having problems send attachments to AOL and Yahoo accounts as they arrive as Winmail.dat even when sent as plain text emails from my outlook.com account. Ok if sent from my Google mail account.
what version of outlook do you have? The outlook.com bug was fixed in build 16.0.8229.2073. You may need to delete the names from the autocomplete list - when addressing the messages, delete the name from the address list and retype the address.