Email blocklists
Email blocklist monitoring
Your sending IP and domain against fifty blocklists.
What it is for
Being listed is the failure with no error message. Your server is healthy, your queue is empty, and a portion of your mail is being dropped silently by receivers who will never tell you. Most people find out when a customer mentions, weeks later, that they never got the invoice.
We check the IP and the domain against fifty lists every hour and tell you which list, so you can go and file the delisting rather than work out where to start.
Like every check here, it runs from Amsterdam, New York and Sydney, and a failure is confirmed from a second continent before anybody is woken. How that works.
What you can set
Everything below is on the form when you add one, on every plan.
- What to check
- A sending IP address or a domain. Both are worth watching: they are listed separately and for different reasons.
On Starter, Pro and Business, checked hourly, and the interval is not adjustable. One check is fifty DNS lookups, and a product that let people run that every minute would be delisted as an abuser, which would make the feature worthless for everybody using it properly.
Questions
What is a DNSBL, and is an RBL the same thing?
The same thing under two names. A blocklist publishes itself as a DNS zone, so asking whether an address is listed is a DNS query for that address reversed under the list's domain. An answer means listed and the answer's value says why. RBL is the older name and you will see both, along with blacklist, which is what most people still type.
Do you check Spamhaus?
No, and the reason matters more than the answer. Spamhaus refuses queries arriving through a shared resolver, which is every resolver a rented machine is handed, and a refused query comes back looking exactly like not listed. Reporting a clean result we never actually got is the one failure this product must not have, so it is out rather than in and quietly broken.
Which lists do you check, then?
Fifty for the sending IP, including Barracuda, SpamCop, SORBS, UCEPROTECT, CBL, Mailspike, DroneBL and SpamRats, and SURBL for the domain, which is a different problem: your domain can be listed from somebody else's botnet while your own IP reputation is spotless. Every one of them is a list a real mail operator would act on.
My IP is clean and my mail still lands in the spam folder. Would this have told me?
Only if a listing was the cause, and often it is not. Deliverability also rests on SPF, DKIM and DMARC lining up, on what the message says, and on the reputation the receiver has built for you privately, none of which a blocklist lookup can see. This catches the listing, which is the cause with no error message attached.
Do you check my PTR and reverse DNS?
Not in this check. A sending IP with no reverse DNS, or with a generic one from your hosting provider, is a real reason for mail to be refused, and it is a record rather than a listing. A DNS monitor on the PTR record, with the name you expect, watches it properly.
How do I get delisted?
Through the list's own form, which is why the alert names the list and the code it answered with rather than saying you are listed somewhere. The check runs hourly, so you hear about it within the hour and you can watch it clear without having to ask anybody.