This Monday morning I was enraged by a note from a marketing consultant on one of the email discussion groups I belong to. She wrote, "I tell my clients to test sending opt-out email because, it might work for them, and why not test it?"

Normally I don't enrage easily - and certainly not over other people's business decisions that are none of my affair.

Plus, I've always believed that picking what level of permission to use is not a moral (or emotional) issue, but rather should be a cold-blooded business decision. Best practice is to research and weigh the risks thoroughly, make the best decision for your particular brand, and then track results carefully.

But, I forgot about email blacklists.

If they blacklist a mailer (which they do both more frequently and more inaccurately than most marketers realize), they generally don't blacklist by mailer name. They blacklist by IP address -- the server that sent the email.

Plus, if the offense appears egregious enough, they blacklist by IP "range" too -- not just one server but many of them.

So, if you send mail through an email service that other mailers use, everyone else's mail will be blacklisted and filtered too.

That's right -- some other mailer's send can cause your mail to be blocked too. I know because it's happened to us, not once but three times.

I've lost thousands of dollars due to blacklisting because someone else thought, "what the heck, let's just test" something that was considered junk by at least one recipient.

So, when you test something risky, such as opt-out, all the mailers who share your email service are forced, unknowingly, to take an equal risk right along with you.

Please, only take risks if you don't use a shared service. Otherwise you're peeing in the pool other kids have to swim in.