A blocklist, alternatively called a DNSBL (DNS Blocklist) or RBL (Realtime Blocklist), is a spam blocking list that can prevent a mail server from sending email.
Where Should I Check for IP Blocklisting?
There are hundreds of DNSBL sources across the internet, which can cause confusion about which actually affect email deliverability. The following major DNSBL providers are monitored and considered reputable by us and other services:
- SpamHaus - One of the largest and most reputable DNSBL. SpamHaus is used by the majority of ISPs and email service providers.
- SpamCop - A DNSBL which is based off reports by SpamCop users.
- Barracuda Reputation Block List - Open source DNSBL service.
- Invaluement - A IP and domain subscription based anti-spam blocklist.
How Can I Detect If Delivery Is Affected by a Blocklist?
Mailgun provides event logs for tracking for each message sent through our service. The event logs are available by logging into the control panel and viewing the Logs (Sending > choose your domain > Logs). Alternatively, event logs can be requested through our Events API. We will provide Failed events when an email could not be delivered to the recipient email server. Clicking the log event will expand the view for more details of the event.
I Detected Failures Due to Blocklisting. What Are the Next Steps?
First, it's highly probable we've already processed the delisting, and are awaiting confirmation of removal from the DNSBL; we have an excellent and highly proactive AUP team monitoring all aspects of our system constantly. Each DNSBL processes removal differently and vary in time range.
To check on the status, or request further investigation of a failed event, contact our Support team via the Support tab in your Mailgun control panel, and please include the full details found in your Logs.