Don’t Pack Addresses in Headers

Hands down, the most offensive way to email a message to a mailing list is by placing all the recipients into a To: or CC: header or both. Not only will this likely mark you as a spammer, but it also risks that your site will become listed at one or more blacklisting sites.

Never send mail to a mailing list like this:

To: list-owner@mailing.list.domain
Cc: bob@a.domain, ben@another.domain, bill@yet.another.domain,
       carrie@somewhere.gov, jose@there.domain, ...
        etc. for hundreds of addresses

There are two serious problems with this approach. First, it reveals all the members of the list to every recipient on the list. This violates the privacy of each recipient on the list. Most who join an organization, or mailing list, expect that their membership will be private and not advertised to others.

Second, messages with too many header recipients (typically more than 25 or so) are consider spam email by many sites. Mailing list messages are not spam email and therefore should never appear to be.

See Internal Mailing Lists on page 485 to learn the correct way to set up mailing lists using sendmail.

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