What to do if your mail is being blocked

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If you are outside Janet and you believe a Janet organisation is blocking mail from you, please read this note before recording a complaint.

A Janet mail server is blocking me. Why?

Many Janet organisations use the Janet DNS deny lists (Spamhaus Zen) to refuse mail connections from listed IP addresses. Janet endorses this use but does not manage the content of the lists concerned.

To find whether your mail server is on the list, fill in its IP address at

http://www.spamhaus.org/sbl/index.lasso (for SBL, XBL, PBL, Zen)

What can I do about it?

You should be able to tell from the above lookup pages which of the lists and component lists you are on. The criteria for listing, and the action you should take, are summarised later in this note (Component lists).

What can Janet do about it?

Janet encourages customer organisations to use the Spamhaus Zen lists. If you believe you are prevented from sending mail because you are listed there (or in the Janet Zen lists which are our replicas), our advice to you is to follow the instructions for the list concerned.

Note that there may be a delay of up to an hour between removal of an entry from the Zen lists and its disappearance from the Janet replica.

If you believe your IP address is not listed and a Janet customer organisation is refusing email from you for some other reason, please contact the Janet Service Desk.

Other causes of email blocking.

Janet provides mirrors of selected DNSBL's, but individual customer organisations are free to make their own choices about which lists they use, and about domains or IP addresses from which they do not wish to accept email.

Many other DNSBLs are available, each with their own criteria for listing and removal from the list

Component lists


  • SBL (Spamhaus Block List) lists the IP addreses of direct UBE sources, spam services and spammers themselves. Anyone on SBL will have to demonstrate that they now follow good practice.
  • XBL (Exploits Block List) lists addresses which are victims of illegal third party exploits, including proxies, worms and trojan exploits. Ensure that your computer or computers are clean of infection and not under the control of an unauthorised third party.
  • PBL (Public Block List) lists IP address ranges whose owners' policy is that they are not expected to be used directly for outbound email. The IP address of your mailer is in a service provider's consumer facilities and it is not expected to connet directly to other people's mail servers. Either send mail through your service provider's outgoing server (possibly called their "SMTP server" or "smarthost") or ask your own service provider for help.
  • DBL (Domain Block List) lists host and domain names used as  references within the body of spam messages. This list can be used in  conjunction with email content scanners to help detect spam.

Zen is the union of SBL, XBL and PBL; IP addresses are in Zen if and only if they meet the criteria for one or more of the other three.

Further information

Spamhaus pages:

One of several lists of other address lists: