Each incoming mail is scanned by our anti-spam filter, that assigns it a spam score value.
If an e-mail is suspect, the anti-spam program tags it as “ [Maybe SPAM] ” and assigns to it a spam score value starting from 3.5.
Depending on your Spam level set using Horde or Roundcube (default 5), the incoming mails will be delivered into the INBOX or INBOX_spam folder.
For example using default settings (Spam level 5):

• an e-mail with spam score value “ 5 ” will be delivered into the INBOX_spam folder, but it is tagged as “ [Maybe SPAM] ” because its value is > of 3.4;
• an e-mail with spam score value “ 4 ” will be delivered into the INBOX folder, but it is tagged as “ [Maybe SPAM] ” because its value is > of 3.4;
• an e-mail with spam score value “ 3 ” will be delivered into the INBOX folder.
  

If you set “ 1 ” as your Spam level a lot of your incoming mails will be delivered into the INBOX_spam folder (LICIT E-MAILS TOO!!!!).
If you set “ 9 ” as your Spam level a lot of your incoming mail will be delivered into the INBOX folder (SPAM MAILS TOO).
So if you wish to change your spam level, choose carefully.