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Some mailbox.org users complain that they receive a lot of spam in their mailbox. We would like to explain the reasons for this, why it happens, and how spam filters work.

If you want to successfully filter out spam, you can use content properties (the word ‘Viagra’ in the subject line) as well as a number of technical properties: Who sent me this e-mail? How does the sender behave? Am I dealing with a normal mail server or a virus botnet? Where was this e-mail sent from?

It’s important to recognize that you’re talking to a spammer (or its software). This is possible to do very reliably and quite easy thanks to special procedures and technical properties. That’s why the content of the e-mail is a secondary concern. A spam e-mail is not classified as such because the work Viagra is in the subject line, but rather, because a spammer sent it. This is only right and important. Providers are not authorized to censor content (for example, ‘No Viagra e-mails from the doctor’); rather, they have to use their skills to detect spammers.

As a result, it is only possible to successfully filter spam by talking to the spammers themselves. All of these important identifying features are lost as soon as the first normal mail server accepts the e-mail, as the e-mail is then forwarded from one clean system to the next clean system and rated unproblematic from a technical point of view.

As a result, the first provider that receives the e-mail is responsible for spam filtering. All subsequent providers can limit the damage and try to ‘save what’s left to save,’ but they will no longer be able to reliably filter on account of the lost technical details. If these providers then tried to compensate for the lost technical information by using aggressive e-mail content filtering, the danger of accidentally filtering real e-mails (false positives) would increase enormously.

Our spam filter has to accept the bulk of the e-mails if, for example, you have a mailbox with another provider (GMX, web.de, a university account, etc.) and you forward all of your e-mails from this mailbox to your mailbox.org mailbox. All of the technical properties related to the spam mailing are no longer available and it is not possible to detect forwarded e-mails based on content features alone.

Please do not complain to us about forwarded (and delivered) spam e-mails from e-mail addresses operated elsewhere. Complain to the other providers. They are the ones who have accepted spam and not filtered it out. They are the ones who should and could have filtered it out. Ask yourself why the questionable spam e-mail was ever forwarded to mailbox.org in the first place.

If you are operating your mailbox.org mailbox simply through forwarding, we can no longer guarantee spam protection that other providers before us carried out carelessly. We repeatedly determine that almost all spam complaints involve e-mails that have passed through to us as a result of forwarding in other mailboxes. In such cases, we can still guarantee 95-percent protection. However, it is no longer technically possible to achieve levels of 99.9 percent and higher that you have come to expect from us.

We operate extremely reliable spam filters and have close to 20 years of experience in this field. As specialist e-mail consultants for anti-spam systems, we are responsible for many companies as well as a number of well-known providers. We know what we can do, and unfortunately, we also know what some major providers, for whatever reason, do not do. Unfortunately, we cannot provide any assistance in such circumstances.