Getting past email blocking

If your mail to other sites is blocked because your IP address appears on DNS based blocking lists, (and you are not spamming) the most practical suggestion is to get a smarthost. You can do this quickly, and no cooperation from DNSBL maintainers is necessary. Your MTA has place to give the name of a smarthost to relay all your outgoing mail to Internet destinations. Your ISP has a smarthost available free for your use, probably named "smtp" or "mail". If you can't find your ISP smarthost name at your ISP web site, here are some web pages with lists of smarthosts by ISP name:

If your ISP smarthost does not appeal to you (perhaps it is on some DNSBLs itself), here are some commercial services in that business:

These are not very expensive unless you have mailing list quantities of mail. I have only been a customer of SMTP.COM. These firms can smarthost for MTAs and MUA, except that Dyndns (now is intended only for individual MUAs. None of these were on any DSNBL the last time I checked, so they do seem to have a way of keeping out spammers and should have good deliverability.

If your problem is an apparently dynamic IP address (one with "adsl","pool", "dynamic", "ppp", "ppoe", etc as part of the hostname) you may want to ask your ISP for an RDNS (Reverse domain name lookup) that implies a non-dynamic address. For example "" looks a lot more stable than "". Although we recognize that the latter could possibly be a static address, it is not practical to use a machine with such a name for outgoing mail because of widespread blocking.

If you are an ISP, then you have a more difficult job. First, stop the spam coming from your system, and change your system rules so that spam is unlikely to come again. This probably means not giving accounts to strangers without ID, limiting the number of messages by user account, or other actions.

Moving your outbound mail server to a different IP address will work for most DNSBLs, but some will list the entire network containing the spamming address if they catch you again. This raises the possibility of other customer's spamming affecting your ability to send mail. A partial solution is to ask your ISP ISP to delegate your address range to you, or you could get your own ASN from ARIN or your local registry. That will help distinguish your MTA from other customers of the same upstream and will protect you from most ASN-wide blocks. However, at least one DSNBL will expand a listing to nearby ASNs with common ownership, so the most effective action is always to find an ISP that doesn't tolerate spammers.

Daniel Feenberg
feenberg isat nber dotte org