How to greylisting
Here is a brief information about the blacklist, whitelist, and greylist.
Greylisting is a method of defending e-mail users against spam. Using greylisting will "temporarily reject" any email from a sender it does not recognize. If the mail is legitimate the originating server will try again after a delay, and if sufficient time has elapsed the email will be accepted.
If email is accepted, the email sender (his IP address) is inserted into the whitelist or into the blacklist in case there is no response.
A blacklist is a list or register of entities or people, for one reason or another, are being denied a particular privilege, service, mobility, access or recognition. As a verb, to blacklist can mean to deny someone work in a particular field, or to ostracize a person from a certain social circle.
A whitelist is a list or register of entities that are being provided a particular privilege, service, mobility, access or recognition. Entities on the list will be accepted, approved and/or recognized. Whitelisting is the reverse of blacklisting, the practice of identifying entities that are denied, unrecognized, or ostracized.
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