Mail.app wants to use only StartSSL Certificate!!

Ok, here i am. I did a certificate on trustcenter.de and imported it in keychain. Mail was initially using it. I don't know why, i decided to try to create and test a startssl one and imported it into keychain too. Now, although Trustcenter certificate is selected in mail preferences and not the startssl one, each time i try to send a mail, it asks me to send it with startssl signature! I already tried to export the startssl one, delete it from keychain and then import it again so mail.app should be using the oldest one in the list. No. It asks me again to send it with startssl one. I'm really really bored. I also tried to set it as not trusted and mail asks me always the same.

How the **** can i tell mail to use only and only trustcenter one?