Removing an unwanted signature in Mail...

[Fishrrman]

First off, this isn't my problem.
Rather, it has been encountered by a friend.
He has an m2pro Mini running Sequoia.
He calls me when he's got a problem, but with this one we can't seem to "get further".

A month or so ago, he received from an oil supply company a contract in pdf format. Rather than print it out and mail it back, he thought he'd try "digitally signing" it and send it back that way. Never had done it before. Things didn't go as planned.

I've never used "digital signatures" before, either, so I have no real expertise in this.
I did some quick research and it looks like to do it properly, you have to have a Mac with a camera. My friend is using a Mac Mini with a Dell display (no camera).

Somehow, he tried creating his "signature" using Mail.app (not Preview while actually looking at the document).

Anyway, things didn't work out.
The document was never digitally "signed". Let's forget about that, because then this problem sprung up:
Whatever he did (he cannot explain nor reproduce what he did to create this result), now all his emails come through with headers that look like this:

(note areas outlined in red).

On a visit, we checked and verified that all "signatures" are now removed from Mail.app's settings. But still, sent emails (from him) display the "unable to verify message signature".

I checked his keychain, and removed what looked like a signature certificate from him that looked like the culprit. But... no change.

Where else can we look where to remove "the cruft" left over from his failed signature adventure?

How can we make Mail.app "forget" that it ever HAD any "signatures"?

 

[HobeSoundDarryl]

After you cleared signatures and keychain item, did you reboot the Mac?

There are many webpages about this. Just type Apple Mail and then unable to verify message signature. Most offer multiple "solutions" that MAY fix it. One in particular looks promising...

1. Click on the “Mail” menu.
2. Click on “Settings” and then “Accounts” tab.
3. Select the account for which you want to disable digital signature verification.
4. Click on the “Advanced” tab and then uncheck the box next to “Verify digital signatures”.
5. Click on “Close” to save the changes.

I worked through the steps to #4 but could not see an "Advanced" tab... but I haven't upgraded to latest macOS yet, still clinging to last update of prior generation until about .5 or .6.

Apples own support forums reference this issue and says the only solution is following what is on an MIT Knowledge Base entry. However, many other posters then chime in thinking this is a bug "somewhere else" manifesting as this message.

And if that doesn't do it, I'd take it into an Apple Store and ask them to fix it.

 

[Fishrrman]

Thanks, Darryl.
Here's the pertinent info (screenshot) from the MIT page linked to above:

I won't know if this works or not until the next visit to the friend's.
Will try to follow up later.

 

[Fishrrman]

A followup:

My friend tried the "MIT solution" referenced above, and that seems to have solved the unwanted signature problem. He sent me a test msg and it no longer has the "unable to verify" notice as illustrated above.

Thanks again for the reply.

 

[!!!]

Heh, never thought about that. There are actually three different kinds of "signature" in mail.

One of them is the simple one, adding your name and maybe phone/email to the end of every message.

The next is the "proper" (technical) definition, where you checksum your message contents and encrypt it with your private key. Doing so means other people can verify that you sent that message and that it hasn't been tampered with.

The third kind isn't really related to mail at all, it just refers to Preview sticking an image of your signature onto a PDF.