Whatever happened to Winmail.dat issues?


Assuming you are a non-Microsoft user - and why WOULD a smart person like you be a Microsoft person? No, seriously, assuming that you are either not a part of the Evil Empire - um, not a Microsoft user, or at least not always a Microsoft user (maybe you have a tablet or a Mac as a second machine), when was the last time you saw a winmail.dat attachment? It's been a long time since I've seen one or had anyone ask me about that.

Google "winmail.dat" if you are a Microsoft user with no non-Microsoft folks in your addressbook and therefore have no idea what I'm talking about.

It seems strange - that used to come up frequently. People would think the file was an attachment they were supposed to open. There actually could be an attachment embedded in there, apparently, but most of the time it's just Outlook formatting junk and of no use to anyone except another Outlook user.

Those Outlook users can control their outgoing format:

Outook mail formatting options

I think maybe Outlook now defaults to HTML rather than RTF (setting it to RTF was what caused those stupid Winmail.dat things). That could explain why I haven't seen any recently. Or if not, a lot of people have changed their settings, which seems less likely.

Some servers like Kerio Connect have a setting to silently decode TNEF (Transport Neutral Encapsulation Format, which is how these things are encoded), so I'd only see this when someone sends something to my Gmail account rather than my normal address. But, I haven't seen one of these in Gmail for some time either: I did a search and the last one I saw was in March of 2009. I forwarded it to myself again to see if maybe Google had started decoding these too, but no, it came through.

Winmail.dat attachment

The last time somebody asked me a question about this involved Apple mail. They use Kerio Connect, so the decoding wasn't an issue, but (according to what Kerio support determined), the Apple Mail itself was at fault:

The problem is on sender's side - he sends the email encoded in proprietary TNEF format from Microsoft Exchange (winmail.dat). Kerio Connect decodes such messages so it can be displayed on all email clients. The message has two identical parts, one in plaintext, one in RTF. Some clients choose to display RTF event if they are not able to do it correctly. Apple Mail and IOS Mail does this. It is already reported to Apple.

I don't know if current Apple Mail has that issue, but sometime later I came across this:

defaults write com.apple.mail PreferPlainText -bool TRUE

That's supposed to tell Apple mail that you want to see plain text emails. I've never tried it, but am also told that if you have this set and DO want to view (for example) an HTML formatted email as the sender intended you to see it, you can use View -> Message -> Next Alternative. I've never tried that either (I'm not a fan of Apple Mail, sorry).

Kerio Connect users only: The Debug log can turn on extended debugging with the Message decoding option. I turned that on and forwarded myself that RTF message that someone had sent me in 2009. The log noted this:

[09/Jun/2013 15:36:21][15379] {msgdecode} TNEF part of message
/opt/kerio/mailserver/store/queue/00/51b4d933-0000013a.eml decoded.

I supposed it might be more detailed had it encountered some problem, so I decided to try that. I downloaded a winmail.dat file and sent it to myself as an attachment. I confirmed that I got the "decoded" result in the Debug log and then tried corrupting the attachment with various permutations of:

echo "abc" | dd of=t seek=1024 count=3 bs=1 conv=notrunc

(See dd - data dumper if you don't recognize what that is doing)

That DID corrupt the attachment, but all that happened was that Connect left it as an attachment and no message was written to the log. Other logs can report TNEF errors, apparently: I saw this in a forum post about a TNEF issue:

[22/Apr/2009 11:29:58] mail_queue.cpp:
TNEF decoding of message C:\Program
Files\Kerio\MailServer\store/queue/34/49ef4604-0000542f.eml failed:
TNEF stream contains unsupported properties

I suppose that the non-reporting of obvious corruption might bother me more if it had not been so long since I have seen any TNEF, never mind something corrupted!

How about you? Do you still see these critters?

Got something to add? Send me email.

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