How to block spam messages?
Blocking messages from anyone not white-listed defeats the point of email, roughly the same way that duct-taping your postal mailbox shut does it for postal mail. You cannot completely filter out spam/junk-mail, because the spammers are constantly working on outsmarting the mail filters. Using a mail client with a spam filter takes care of some of the spam, but you still have to check for false positives, i.e. legitimate mail that was filtered out as spam due to how you have trained your mail client to recognize junk-mail messages. My advice is that you ought to have two sepeate mail addresses – one public and one private. The public one can be used on public forums, discussions and website sign-ups where you are uncertain of the intentions of the owners (adult sites are one such). Any free mail system will do, like yahoo mail, hotmail and gmail, though the latter is preferred due to seemingly outstanding spam recognition features. The private address can be given to trusted friends an