Low complaint rates are not always good

Digging another old blog post out of the archives. In November 2011, I talked about how part of the Holomaxx complaint against Microsoft and Yahoo said that their complaint rates were below 0.5% and 0.1%. The argument was that if their complaint rates were low, then the mail must not be spam.

Specifically, HolomaXx alleges, its Microsoft complaint rates have been consistently at or below 0.5 percent and its Yahoo complaint rates have been at or below 0.1 percent.
Spam-complaint rates are a significant metric ISPs use to determine if incoming email is wanted by recipients or not.

Senders still seem to focus on the complaint rate. The problem is they don’t understand how ISPs measure the complaint rate. First off 0.5% is actually a high complaint rate. More importantly ISPs only allow complaints for mail that makes it to the inbox. If mail is blocked during the SMTP transaction or filtered into the bulk folder, users cannot complain.
I’ll say it again, because it is critically important to understand.
Bad senders who do not get email to the inbox have very low complaint rates.
Why? ISPs measure complaints as a percentage of the emails that make it to the inbox. If mail is not hitting the inbox then the complaint rates are zero.
I understand this is a bit of a catch 22, in that to get a good reputation you need to get mail to the inbox and to get mail to the inbox you need a good reputation. But I hear a lot of spammers tell me they absolutely can’t be sending spam because their complaint rates are so low and it’s just not true.