I have a mail server running Debian Lenny with Postfix and Dovecot. I send and receive emails without any problems with most of my contacts using Google Mail or Yahoo Mail but some of my contacts will not get my emails.
I do receive a undelivered mail report saying: "firstname.lastname@example.org: Recipient address rejected: "DOBLOCK residential dynamic ip space with zombie activity" (in reply to RCPT TO command)"
I am able to send these contacts emails using Google Mail so I assume the problem is with my server setup. What exactly is wrong with my setup? How can I fix it?
Thanks for your help.