Broken Attachments in Microsoft 365 webmail if GPG signed S/MIME

macmedix's Avatar


26 Nov, 2013 09:03 PM

Which of our tools is giving you problems?

GPGMail 2.1 Build 601

Please describe your problem. Add as much detail as possible.

When sending a SIGNED email with a 1 or more attachments, Microsoft 365 Outlook webmail reports that it can not read S/Mime and therefore NO attachments are available. So essentially just signing an email (the default) makes all attachment broken for users of MS365 webmail.
If I send another email that is not signed, but does include an attachment, MS 365 Webmail can display the attachment, no problem.

Please describe what you did expect instead

I expected that signing the email would not break the attachments for people using MS365 webmail. I would expect that even if the signature was unviewable, that the attachments would not be affected.

If you remember, please describe the steps leading up to the problem

Using default GPG settings, send an email with an attachment to anyone who uses MS 365 Outlook WEBMAIL. (I haven't tested desktop mail, just noticed with that webmail) Sending an signed email without an attachment is received OK, the text displays, but webmail reports that there is an S/Mime attachment that is unviewable by MS 365 webmail.
See attached annotated screen photo of MS 365 webmail.

  1. Support Staff 1 Posted by Luke Le on 26 Nov, 2013 09:17 PM

    Luke Le's Avatar

    Hi Mac,

    this is clearly a bug of office 365 and it would be best to bring it up with Microsoft.
    You could enable inline PGP, in wich case the text is wrapped in a signature and no attachment is created,
    but that's not encouraged, since the signature often breaks due to manipulations by SMTP servers and attachments
    are NOT encrypted, only the message body if you choose to encrypt.

    The following article describes how to enable inline PGP if you still want to try that:

  2. 2 Posted by macmedix on 26 Nov, 2013 09:51 PM

    macmedix's Avatar

    Hi Luke, Yeah, I figured as much. But I also was thinking that maybe the GPG team would be more responsive & produce better quality product. :-)

    At this time, I am just signing emails, not encrypting. So any solution is welcome that allows the email to be signed without breaking the attachments - no matter how lame the recipients webmail is.

  3. 3 Posted by macmedix on 27 Nov, 2013 01:46 AM

    macmedix's Avatar

    I followed the link Luke provided & tried enabling inline PGP, but that seems to knock out any other attachments. The recipient does not even know I included an attached file. So Thanks, but not a good solution for emails that include an attached file such as a picture or document. It appears the only current solution is to turn PGP signing off when the recipient is using MS Outlook Web Mail, but of course I have no way of knowing. Since I am just digitally signing emails not encrypting, and since a client just switched to using MS 365 cloud email, switching off pgp may be my only available option when I am sending files.

    FWIW, I did file a bug report with MS, but I doubt they care about Mac OSX nor Linux, nor ensuring their web app is compatible with digitally signed emails. (sigh).

  4. 4 Posted by macmedix on 27 Nov, 2013 06:16 PM

    macmedix's Avatar

    I got a reply from MS Support. They don't care. It's not a tech support issue.

    This is Chris Munroe with Exchange Online support in regard to service request 1224977378, regarding an issue with viewing s-mime attachments. I apologize about any inconvenience, and have reviewed your update. As we both agree this is by design with the current version of Exchange Online and cannot be resolved by technical support. If you would like to suggest this feature added to Exchange Online please utilize the feedback link from within Outlook Web App by clicking on the question mark toward the top right of the screen. This service request will be closed as the feature is unsupported currently.
    Thank you for contacting Microsoft Online Service support,

  5. Support Staff 5 Posted by Steve on 29 Nov, 2013 11:36 AM

    Steve's Avatar

    Wow, nice support from MS. Macmedix: As Luke pointed out, OpenPGP/Inline currently does not support attachments.

    Since it is a un-documented standard it isn't really encouraged to be used. I'm not even sure if there's anything on our side we could do to improve the situation except for improving OpenPGP/Inline.

  6. Steve closed this discussion on 07 Jan, 2014 03:20 PM.

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