jarkkolinnanvirta wrote:
But this problem did not exist a few weeks ago.
Did you modify any config files on this server? Let's see whether it impacts spam scanning or not.
It's hard to say why it occurs, spammers are learning and improving too. If those spams have the same finger, e.g. same sender domain, same subject, etc, you can add/update SpamAssassin rules to block them, or blacklist sender domain/IP directly.