Experiences sending email with a Secure Certificate

Question

Hopefully this post will save others some of the time it's taken me to discover the following.
_Cause of my confusion with Mail 4.1, Address Book and Keychain Access Utility:_
1) Address Book shows its "starred ticks" against both my mac.com and me.com email addresses and when clicked these ticks display valid certificate details .... so you'd be forgiven for thinking that you could send digitally signed emails from these addresses ... but you can't ... not until you've taken one of the two options below - and each option has different consequences for your email recipients.
2) Discussion threads from previous Mac OS X releases suggest you can use iChat Encryption certificates for signing and encrypting emails. I don't think you can do this (anymore). I could make the iChat certificates "Always Trusted" in Snow Leopard's Keychain Access Utility but Mail would still not recognise them as being valid for authenticating outgoing (digitally signed) email.
In other words the "starred ticks" didn't appear in the outgoing message composition window heading as it should do.
Solutions:
I thought you'd be interested to know what I found out after experimenting with:
1) A Self-signed certificate created in the Mac OS X Keychain Access Utility
2) A Secure email Certificate obtained (for free) from C.O.M.O.D.O
[I looked at Thawte and VeriSign but Thawte are no longer doing Personal email certificates and are passing all their existing ones over to VeriSign this month (Oct / Nov 2009). Personal Secure email certificates are a bit harder to find on the Verisign website and a certificate costs $20 for a year and seems to offer no more "trust" value than a C.O.M.O.D.O one ... which is free and relatively easy to find.
_The experiment:_
I found that a Windows Outlook Express recipient would be notified that:
1) the self-signed certificate "could not be trusted" but that
2) the one simply obtained from C.O.M.O.D.O was accepted (without any warning) as trusted by a known CA (Certification Authority)
You could argue that both methods are pretty well identical in terms of real-world authentication value but, to the recipient, they both look very different:
1) a warning dialog obscures the email and reports that the self-signed certificated appears untrustworthy
2) the CA-issued one "Inherits Trust from Issuer" (according to Outlook Express's inspection of the certificate details) just displays a little rosette symbol and thus gives confidence.
In fact, the C.O.M.O.D.O. process involves emailing the applicant her certificate downloading instructions. In this sense the email address associated with the certificate is authenticated. That's the most authentication one of these certificates can really support, anyway.
_Obtaining the CA-issued certificate:_
It's an easy two-step process to request and download the certificate from COMODO's web site. The certificate is automatically installed into Mac Keychain Access Utility upon Safari download.
Hope this helps someone!

Answer 1

The solution is when you started in Firefox to collect all these requested certificates with the same browser.
Then to export (Preferences > Advanced > Encryption > View certs > Your certs > Create backup of all...) the certs to a PKCS12 file; and import that file into keychain (by double clicking within Finder)