Everything was working fine, no changes to DNS or Email Server settings. Then we got the error below when some users (not all) send emails (some user and domain names and ip's have been changed).
This happens to some email users only.
De: MAILER-DAEMON [mailto:MAILER-DAEMON] Enviado el: lunes, 25 de junio de 2012 01:49 p.m. Para: email@example.com Asunto: Undelivered Mail Returned to Sender This is the mail system at host mail182-ch112-RR.bigfish.com. I'm sorry to have to inform you that your message could not be delivered to one or more recipients. It's attached below. For further assistance, please send mail to postmaster. If you do so, please include this problem report. You can delete your own text from the attached returned message. The mail system <virgilio@sent_to_domain.com>: host zsca-138961-mail2.customer.somethingbridge.com[188.8.131.52] said: 554-Transaction failed (id=4FE8B30610BE0008), maximum 8 recipients listed below: 554-Address:virgilio@sent_to_domain.com Server:999.551.11.130 Command:EODT Error:554 5.7.1 Message refused by DNSBL check. bl.spamcop.net / 5184.108.40.206 This email has been rejected. The email message was detected as spam 554 Transaction failed (in reply to end of DATA command)
What could be the source of the error?