S/MIME encryption not working

I would be grateful if someone would try to help me sorting this out. Perhaps I should give some more details on the problem/my setup?

I'm running Snow Leopard. As mentioned above, signing seems to work but not encryption. In Apple Mail both signing and encryption works so I guess that means the certificate is installed correctly.

The error message you get says that MailMate is providing an invalid parameter, so let's try finding out what that is.

First enabled debug output in the Terminal:

defaults write com.freron.MailMate MmDebugSecurity -bool YES

Then launch MailMate from the Terminal:

/Applications/MailMate.app/Contents/MacOS/MailMate

Try encrypting and provide the output in the Terminal. By email if you like (“Help ▸ Send Feedback”).

Thanks in advance.

Thanks for your quick reply.

Here is the output:

Searching for certificate for ********  
 Result: Failure
 Detail: Failed to find certificate to encrypt for **********.
 Detail: One or more parameters passed to a function were not valid. Error code: -50
2013-11-22 12:16:02.207 MailMate[24211:903] Warning: Unknown security problem (S/MIME): unknown  
2013-11-22 12:16:02.276 MailMate[24211:903] Warning: Unknown security problem (S/MIME): unknown  
2013-11-22 12:16:02.420 MailMate[24211:903] Warning: Unknown security problem (S/MIME): unknown

I do have a certificate for the email address in keychain and it works in Apple Mail. I did however have an issue with MailMate trying to use an old expired certificate instead of a new one which I solved by deleting the old certificate (which isn't ideal obviously but it was a certificate that I hadn't used anyway so not an issue). Could it be that MailMate is still trying to use the deleted certificate instead of the new one.

The odd thing is that signing works fine...

Actually just tried with another email address for which I have not had the problems above with an old certificate and same issue.

No, signing works fine which means your certificate is fine. When encrypting, you need the certificate of the recipient. This is what fails to work correctly. There is some indication that the problem is not really that it's missing: “One or more parameters passed to a function were not valid.”

It seems the only parameter is ********. Anything special about that? Can you send the address to me by private email? Are you sure you have a certificate for that address?

Just sent you an email from the address in question. Nothing special with the address as far as I know. Also signed the email so I guess you could try to encrypt an email on your side with that certificate.

Have tried with two different recipient addresses. Same problem. Both certificates work fine in Apple Mail.

I realise that I need the recipient's certificate for encrypting and my own for signing and I think I'm doing that part of it correctly, so don't think the problem lies there.

Which version of OS X are you using?

Using 10.6.

Added your certificate and tried to encrypt. Same problem.

10.6 is not officially supported, but I'm not sure the problem is related to 10.6. Do you have any way to check if you have the same problem on 10.7+?

Ah, didn't even realise. :) It works perfectly on 10.6 apart from this issue.

No, unfortunately not now. But if that's the cause, it's not a big deal. Upgrading in a couple of weeks. Could follow up on it then.

Updated to Mavericks and it seems to be working fine now so guess it was due to Snow Leopard.