1. Check against Whitelist;
2. Check against Blacklist;
3. Start filter engine;
4. Judge as spam/legitimate.

Additional manual adjustment may be necessary.

This is how Lockspam works. As the picture below shows, Lockspam Pro scans your mail by 8 steps:

The Basic filtering processes mainly compare the sender's e-mail addresses to your Allowed or Blocked List and words in mail contents with your approved or blocked keywords.

While the Advanced filtering processes is planned for probable junk mails. In Lockspam Options > Filters > Advanced Filters, you will see Polesoft's advanced anti-spam technologies: