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Signed emails appear blank in Gmail

An email sent to Gmail appears blank to the receiver with only a .p7m file – why?

If you send your emails with a digital signature they might appear ‘blank’ to a Gmail receiver … something like this:

Gmail - signed message appears blank image from Signed emails appear blank in Gmail at

The above message had HTML text in the message body but neither are showing up in the Gmail web browser view. There’s only a small ‘p7m’ file which is the S/Mime digital signature.

Here’s the same message displayed in Outlook with an IMAP connection to the same Gmail account.

Outlook - same signed message appears OK in Outlook image from Signed emails appear blank in Gmail at

The problem is not the message, it’s how Gmail in a web browser handles the display of the content. For some reason, Gmail’s web browser code doesn’t display a signed message properly. A signed message isn’t encrypted so there’s no good reason for the message not to show up properly.

Happily, the Outlook developers are aware of this and other situations where a signed message isn’t displayed properly by the receiving software. In Outlook 2013 and Outlook 2010 go to File | Options | Trust Center | Trust Center Settings | E-mail security and ensure that the setting ‘Send clear text signed message when sending signed messages’ is checked (as well as ‘Add digital signature to outgoing messages’). In Outlook 2007 go to Tools | Trust Center | E-mail security to find the same option.

Outlook - add clear text to signed messages image from Signed emails appear blank in Gmail at

(This Outlook dialog box hasn’t changed in six years and three versions of Outlook – an indication of how little effort Microsoft has put into signed and encrypted emails within Outlook)

Now, with the clear text version sent in the same email, any email software or web page should be able to read the message. The Outlook setting is a little misleading because the words ‘clear text’ imply that only text is sent when, in practice, HTML and embedded images are included in the ‘clear text’.

Here’s how a message with clear text version shows up in a Gmail web page.

Gmail - signed message with clear text appears normally image from Signed emails appear blank in Gmail at

As you can see, the digital signature is there in a small smime.p7s file that the recipient can ignore. All the text and embedded image is in plain view to the receiver.

If you want your messages to be more secure, get the digital certificate of your correspondent so you can encrypt emails in both directions.

It would be nice if Google and other email clients improved their support for digital signatures but in the meantime senders should include a clear text version to save hassles.

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