Email Digital Signature causing blank email?



  • I'm trying to troubleshoot an issue that sometimes occurs when a user emails, in this case, a major bank.

    The user has digital signing on by default, so when the user sends an email to this bank, they say that the email body is blank.

    This doesn't make sense because nothing is encrypted. And if you send a digitally signed email to something that doesn't support it, such as web gmail, it (the signature) just shows up as an attachment.

    So I'm wondering if this bank may for example be blocking ALL email content if it contains a digital signature (or attachment if it's not supported)?

    I think the issue does not happen if the user de-selects the "sign" button, turning off the digital signature before sending the email. Still waiting to hear back, but getting this out there awhile.



  • @scottalanmiller , you've worked with a lot of Financial institutions I believe... can you say if it's common to block email content if there exists an unknown attachment type such as an email signature?


  • Service Provider

    @Tim_G said in Email Digital Signature causing blank email?:

    @scottalanmiller , you've worked with a lot of Financial institutions I believe... can you say if it's common to block email content if there exists an unknown attachment type such as an email signature?

    Yes, absolutely.



  • There was a user of Spiceworks Inventory that had the same issue when someone with a digital signature would send emails and the ticket will not be created unless it was plain text. I would maybe make a rule on the email system to send plain text to that specific domain recipients.



  • is Mimecast anywhere in the chain? At one time we were having a similar issue where Mimecast was stripping emails with digital signatures. This was us sending out through Mimecast (using them as our smart host) I do not remember if the email received by the vendor was blank, or if it contained a message about an invalid attachment. I had to open a support case with Mimecast and there was a gateway setting (Sorry I do not remember the exact setting) we had to change. Good Luck


  • Service Provider

    @dbeato said in Email Digital Signature causing blank email?:

    There was a user of Spiceworks Inventory that had the same issue when someone with a digital signature would send emails and the ticket will not be created unless it was plain text. I would maybe make a rule on the email system to send plain text to that specific domain recipients.

    We've had something like that in the past, too.



  • @jt1001001 said in Email Digital Signature causing blank email?:

    is Mimecast anywhere in the chain? At one time we were having a similar issue where Mimecast was stripping emails with digital signatures. This was us sending out through Mimecast (using them as our smart host) I do not remember if the email received by the vendor was blank, or if it contained a message about an invalid attachment. I had to open a support case with Mimecast and there was a gateway setting (Sorry I do not remember the exact setting) we had to change. Good Luck

    Not on our end. It's just straight Outlook and O365. Nothing in O365 security that I've seen.

    I'm still waiting to hear back from the user if turning off the digital signature fixes the issue.



  • Had an issue when a colleague and his whole dept had made a signature which includes an image. However, a forward or reply, makes the email visible. Had traced down that that image caused the blank mail so I re-created the image (by print screen) then inserting it back.

    We were using Zimbra, BTW.


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