What this analysis does
Enter a sending address or a hostname to resolve. Mailybox queries the major public DNSBLs that answer shared resolvers — SpamCop, Barracuda, PSBL, UCEPROTECT, DroneBL, Mailspike and others — reports each listing with its return code and stated reason, and checks the PTR record because missing reverse DNS causes rejections independently of any list. Lists that refuse public resolvers are named rather than silently reported as clean.
A blocklist listing turns a working sending address into one that is rejected or throttled by every receiver consulting that list. Knowing which lists hold the address, why, and what each list requires for removal is the difference between a quick fix and weeks of deferred mail.
How DNS blocklists answer
A DNSBL is queried by reversing the address and looking it up under the list’s zone. A listed address returns a loopback-range answer whose last octet encodes the reason; an unlisted address returns nothing. Many lists also publish a TXT record with a human-readable explanation and a removal URL, which the checker reads and shows.
Because the mechanism is DNS, the result depends on the resolver used. Several important lists — Spamhaus above all — refuse queries from shared public resolvers and return an empty answer, which is indistinguishable from "not listed". The checker excludes those lists explicitly instead of reporting a false clean result.
- Return codes in 127.0.0.0/8 indicate a listing; the last octet is the reason class.
- Empty answers mean not listed on lists that answer this resolver.
- Spamhaus, SURBL and URIBL are excluded by design; check them directly.
Fix the cause before requesting removal
Listings have causes: a compromised account or host sending spam, an open relay, backscatter from bouncing to forged senders, mail from an address with no reverse DNS, or a hosting range with a bad reputation. Requesting delisting before the cause is fixed produces a short reprieve followed by a longer listing.
Each list has its own process. Some delist automatically after a quiet period, some offer a self-service form, and some require an explanation. The listing reason and the TXT record usually point at the right path.
Check PTR and HELO for the same addressTrace where spam from the address originated
Lists are not the whole reputation picture
Gmail, Microsoft and Yahoo rely primarily on internal reputation systems that no public list exposes. An address clean on every public list can still be throttled by a large provider because of complaint rates or sending pattern, and the reverse is also true. Use public lists to catch the obvious problems and provider postmaster tools for the rest.
Shared sending infrastructure complicates attribution. If the address belongs to a platform rather than to you, the listing may be caused by another customer, and the platform is the party that has to act.
Check provider sender requirementsRead the reverse DNS guide
Example: a new server with no reverse DNS
Evidence supplied
A freshly provisioned sending address with no PTR record and a short sending history.
How to read the result
The address is listed on the no-PTR list and clean elsewhere. The findings identify missing reverse DNS as both the listing cause and an independent rejection risk, and point at the hosting provider as the party that publishes PTR records.
Known limits
- Lists that refuse shared resolvers are not queried; absence from this result is not proof of absence from those lists.
- A clean result covers public lists only; provider-internal reputation is not visible.
- A query time budget applies; on slow networks the last lists may be skipped and are reported as such.
Common questions
Why is Spamhaus not included?
Spamhaus refuses queries from public resolvers and returns an empty answer rather than an error. Reporting that as clean would be misleading, so it is named as excluded. Check it at spamhaus.org.
I am listed. What first?
Identify and stop the cause — compromised account, open relay, missing PTR — then follow the removal process in the listing reason. Delisting before the fix does not last.
Does a listing affect all my mail?
Only mail from the listed address to receivers that consult that list. The impact depends on which lists and which receivers.