Cameo can now make routine checks to see whether outgoing mail servers have been put on a spam block list. Checks are carried out daily at around 07:45. If the check discovers new block list entries, it posts a reminder message with details.


Many smaller email services bounce email if the sending mail server is listed on one or more of a large number of email block lists. (Larger services, like GMail, have their own proprietary spam detection methods so do not use public block lists). Therefore mailshots sent via Cameo may fail to reach their recipients if its mail provider ends up on one of these lists.

While Cameo picks up message individually bounced for this reason, a pro-active check is also useful. There are lots of third-party services (such as mxtoolbox) that check a range of block lists, varying from free to very expensive, but it turns out it is quite easy to check for ourselves.

Block lists

Block lists are a very blunt instrument. They produce a lot of collateral damage.

As most mail is sent from servers shared by many senders, it works like the classic teacher’s unfair punishment: you’ll all stay behind until one of you owns up. Senders constantly get blocked because of others’ activity on the sending server.

Most block lists add a server if they get mail from deliberately planted honey trap email addresses, which can only have been obtained by underhand means. However, some will block on the basis of a few people reporting the server as sending spam, which is rather subjective.

Block lists work on the IP address of the sending server. Some mail providers use more than one IP address to send mail, so it often happens that some emails will get through but others won’t, to the same provider.

Pretty much all providers that use block lists do not offer any facility for individual users to make exceptions. All mail from a listed IP is bounced unconditionally. Providers reason that making exceptions by sender does not work as sender address is easy to forge. Even though more recent technologies, like Sender Policy Framework (SPF), make forging sender address much harder, providers have not changed their attitude.

Most block lists automatically remove IP addresses from their listings a few days after they last detect spam. Most also offer manual removal requests for owners of disputed addresses.

What does Cameo check?

Cameo checks about 50 block lists. However, mail clients use a few block lists much more widely than others. If a server ends up on one of these lists, it potentially affects lots of recipients:

Cameo carries out checks only if it is configured to do so. This has to be done by the Cameo administrator.

The first check to happen will pick up any existing blocks.