I manage a Linux server that functions as an email server using the
free and open source software (FOSS) package
sendmail.
I provide a mechanism through the server for someone who has
Verizon as his
Internet Service Provider (ISP) to send monthly newsletters
by email to an organization that has about thirteen hundred members on its
email distribution list, since he can't send to that number of people through
his ISP-provided email service. I do so by providing an
email alias
on my server, e.g., thelist@example.com that he puts in the
BCC line of his email. The alias is stored in /etc/aliases
and points to a text file containing the list of all members' email addresses.
So his ISP-provided
SMTP server sees only the one address, thelist@example.com,
which results in an email message to the server I manage that then translates
that address into the approximately 1,300 email addresses of members and sends
the newsletter to all members.
But this month the user reported he had sent the
message, but it had not been delivered to recipients. I first checked the
server's mail log, /var/log/maillog, for any occurrences of his
email address for the day he reported the problem. I use several free
DNS-based
Blackhole List (DNSBL) services to reduce the amount of
spam that
reaches user's inboxes, so I suspected that one of those services had blocked
email from the SMTP server through which he was sending his message, even
though I had whitelisted his email address quite some time ago by
adding a line like the following one to /etc/mail/access and
then running the command makemap hash /etc/mail/access
</etc/mail/access.
slartibartfast123987@verizon.net OK
I didn't find any references to his email address in the /var/log/mail
file, so I asked him to resend the message. I still didn't see any
references to his email address in the /var/log/maillog file,
but I did see that SORBS had blocked email from an
America Online (AOL)
server at the time he sent the message.
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