So this past weekend I went to visit my Aunt & Uncle in Harrisonburg, VA. While there, my Aunt tells me she can’t send email thru my server which I was fairly certain was once again, “user error.” Come to find out. It was a misconfiguration on my part! Ah ha!

Long story short, I had reconfigured my email server about two months ago and added a DNSBL ( to my sendmail features and it was blocking her from relaying email thru my sendmail server. I simply had to add…


… to my file and restart the service. (NOTE: On CentOS 5.0 if you restart the sendmail service it will check your & files and do a ‘make -C /etc/mail’ for you if the is newer.)

Now, Sendmail will wait on the DNSBL and give the user a chance to authenticate first which will allow them to then bypass the DNSBL. Seems her residential comcast IP Address was added to which is commonly done to blocks of residential user IP address spaces to prevent spam.