From Computer Tyme Support Wiki
So - your email bounced and you ended up here. If your email bounced wrongly we want to fix that. but in order to do so we need as much information as possible from you so that we can track down the problem. So we have set up a special domain with no spam filtering to receive any kind of problem messages. So if you can't forward the mail directly to us because the message bounces, send to it the email address email@example.com with the subject containing the words FALSE POSITIVE. Note the email goes to .org and not .com. Our regular email address is firstname.lastname@example.org .
Why did my email bounce?
You are probably wondering, why did my email bounce in the first place? The short answer is that spam filtering is very difficult and it's impossible to get it right all the time. We could quote you amazing statistics about the accuracy of our system but the truth is that there is a huge amount of spam that's really easy to catch that makes all of us in the spam filtering business seem like we are doing a really good job. But what it comes down to it, none of that matters because your email bounced and you want to know why.
Our filters count mostly on the behavior of the spammer more than the content of the message. Generally it's not as much about what you are saying than it is about how your server is sending it. There are a lot of severely misconfigured servers out there. Even large ISPs (like Comcast in particular) who don't know how to set up reverse DNS correctly. As a result some good servers appear to us to be like spammers.
What we can do however is to put that server in some sort of exception list that bypasses certain tests for specific hosts. This will allow a misconfigured server to communicate properly with our system. And if that is the case we want to fix that.
Sometimes it's not our server that bounced the message
Our spam filtering service Junk Email Filter is a front end spam filtering service. Email comes in from the internet, we clean it, and pass it on to the customer's email server. Often the customer has little or no control over their own email server because they are hosted by a hosting company that does it for them. Many of these hosting companies have their own spam filtering rules and they reject email that we consider good but they refuse to accept. If the other server rejects the email it often looks like we rejected it. So pay attention to the specific error message and if it indicates that the remote server rejected the email, that's not us rejecting it.
However, having said that, sometimes it is a problem that we can fix so we still want to know about it. We might have to get the receiving server to whitelist our hosts. Or maybe we are presenting the message wrong and it's something we can fix on our end. We will work with you to get the email through.
There are several server configurations that are potential problems that are difficult to work with. The email SMTP specifications are a set of rules that govern how servers are supposed to talk to each other when delivering email. However many servers don't follow these rules and therefore create problem for the rest of us. If you are a hosting company then please follow the rules.
Additionally there are spam filtering technologies that are just bad ideas and should not be used. Some hosts use these out of desperation in their fight against spam. Some technologies stubbornly refuse to go by the rules and they create problems for the rest of us.
Qmail is a popular MTA (Mail Transfer Agent) but it has a serious flaw where is doesn't obey the rules when it comes to retrying other servers when it receives a temporary error. Domains advertise multiple MX records with priority numbers. The higher the number the lower the priority (go figure). So mail servers are supposed to try the lowest MX record first, then if that fails try the higher numbered MX servers.
Qmail is written so that if the lowest MX record returns a temporary error then it refuses to try any of the other MX records and will continue to talk to the same server till it times out and reject the email. There is a patch available to fix this by the author of Qmail refuses to include it in the distributed product. If you must use Qmail we encourage you to use this patch. If you are selecting a MTA, Exim is far better.
The problem this creates is that suspicious hosts are deferred on our lowest MX but accepted on the second MX. So huge amounts of spam are turned away while good email is only temporarily rejected but will be accepted if the retry on the second level that has different rules. Qmail doesn't return and therefore isn't compatible with this system.
Most Qmail is accepted as long as they play by all the other rules. But if the server has a second problem like no reverse DNS or is in a dynamic IP range then the mail doesn't go through. We can fix this individually by putting the IP address in a list that avoids some standard tests. But un till this is done mail will never make it through.
If this is the problem then send a message to email@example.com with the subject FALSE POSITIVE so we can see the IP address of the problem server. Then we can search the logs by IP address and see what the problem is.
SPF is hopelessly broken and needs to die!
The technology Sender Policy Framework (SPF) was an attempt to be a spam blocking technology. The promoters of this are backing away from the spam fighting position because apparently they realized that it is useless against spam. The problem with SPF is that it breaks email forwarding.