Is your server
on a blocklist?
Check whether an IP address or domain is on anti-spam blocklists (Spamhaus, SpamCop, Barracuda, SURBL…), with reverse DNS (PTR), network owner, ASN and country.
Examples: google.com wikipedia.org github.com
Deliverability and reputation
The three conditions for your email to reach the inbox.
A single Spamhaus listing is enough for many providers to reject your email.
The sending server’s address must have a reverse name that points back to the same address.
SPF, DKIM and DMARC prove your messages really come from you: test them in the Email security tab.
FAQ
What is a blocklist (DNSBL)?
A list of IP addresses or domains that sent spam or hosted threats. Mail servers check it before accepting a message: a listed address has its email rejected or sent to spam.
How do I get off a blocklist?
Fix the cause first: hacked email account, abused contact form, infected server or open relay. Then request removal on the list’s website (“Delisting” link in the table). Some lists remove the address automatically after a few days without new spam.
Why does reverse DNS (PTR) matter?
A server that sends email must have a reverse name that points back to the same address (FCrDNS). Without it, Gmail, Outlook and most providers reject or flag the messages as spam. Reverse DNS is set at the host of the IP address.