Blocking on account of the address of the computer delivering mail
The blocklevel can be adjusted by every user via the Do It Yourself website. When an email arrives at the science mailserver the server instantly checks whether the mail address of the recipient exists and whether the recipient has a block level that includes the IP-number of the computer that tries to deliver the mail. Otherwise the mail is not accepted. If the mail would be blocked by a higher block level, the mail is accepted, but sent forward with a mail-header-line: "X-Would-Be-Blocked-By:".
There are four block levels: 'none', 'light', 'medium' and 'heavy', where 'medium' is the standard and recommended value.
none: no blocking takes place.
light: blocking by using the following lists:
whitelist.sci.kun.nl: C&CZ's own white list: machines that are or have been listed on blacklists, but a lot of our users like to receive mail from. The list contains at the moment (luckily) few entries: a list server of Surfnet and the spamprovider of the RadboudUMC.
blacklist.sci.kun.nl: C&CZ's own black list: machines that are not (yet) a problem for others, but are for C&CZ. The list contains at the moment (luckily) few entries, mainly machines that have in the past bombarded C&CZ mailservers with spam and/or viruses.