Mail on OS X: Choose which X.509 certificate to use for signing mails I've got multiple X.509 certificates from different CA's for different purposes -- for example, one from CAcert.org, and another one from my university. Both have different advantages and disadvantages, and I want to decide which one to use in a by-case manner.

Sadly, I cannot find any preferences, not even for selecting a default. In the account settings there is an option for a TLS certificate, but this is only for authentication against the mail servers. How to either


select a key/certificate when composing an email (preferred) or
select a default certificate per mail address or give some certificate ranking?


Currently my only option is removing the one I don't want to use which is rather frustrating.
You can exactly specify the certificate to be used for sining outgoing emails by following these steps:

Open your keychain. Then right click on the list of certificates and pick the first item on the context menu (In English it is labeled New Identity Preference):



Then type in your email address and select the certificate from the drop down box to use for that address:



The next email you send from the email address typed in above will be signed with the selected certificate.