1. OK, a language problem 👿:
iOS is the Operating System on iPhone, iPad.
OS is the Operating System on a Mac computer (iMac, MacBookPro, MacBookAir).
At the bottom of your first message is "MacBook Pro, Mac OS X (10.6.6)", which is information that you put in when opening a "profile" when you decided to participate in the Apple Discussion Forum and posted your question, click on your name (the blue lettering above your message and you will go to your profile.
2. Click the little apple icon on the left above side in the top menubar, then choose "about this mac": you will see a short description of your mac: MacbookPro probably, in that field you also see the Operating System name and version, if not click "more info". Give us here the info, about your mac and your operating system.
3. the two links that I gave you are well readable, look to the passages that refer to your operating system and do what it describes.
4. Can you disable SpamSieve for the moment, to see if that helps, if you can not disable it, uninstall it (you may always reinstall).
Lex