[Greylist-users] Comcast & Greylisting

James J Dempsey jjd+greylist at jjd.com
Thu Nov 30 10:16:53 PST 2006

Jim Hermann - UUN Hostmaster <hostmaster at uuism.net> wrote:

> I whitelist these comcast.net blocks:
> acl whitelist addr     # comcast.net (mailfarm) - jwh
> acl whitelist addr   # comcast.net (mailfarm) - jwh
... (and others) ...

and Dave Warren <maillist at devilsplayground.net> wrote:

> You don't need to whitelist them completely, just bypass greylisting --
> greylisting is useless against legitimate servers, if you KNOW a server
> is going to retry you may as well not bother greylisting it and save
> both of you a little bandwidth.

I have a couple comments.

I have lots of friends and users on comcast, don't have comcast's servers
whitelisted but I don't recall ever having trouble with incoming comcast
email.  I wonder why others have had this problem and I haven't.  Perhaps it
is regional?  (I'm in New England.)

Secondly, while Dave is correct that if an SMTP client follows RFC822
properly and retransmits, then it does no harm to whitelist that client, is
Jim Hermann sure that within all of those IP address ranges there are only
valid SMTP servers and not spam-bots?  If you are whitelisting all of
comcast's IP space, including home cable modem users, then you are almost
certainly eliminating the effectiveness of greylisting against spam-bots
within Comcast's network.

If I calculate correctly, there are 2048 individual IP addresses within the
ranges Jim specifies.

                       --Jim Dempsey--

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