Ok, so this is why spam filtering doesn't work. Filtering only masks the problem. Eventually you can't tell who is friend in foe.

My case in point:

Me: I tried to email my printer with a new spec so I can pay them to do work for me.
Nauticom: The email bounces back to me with this message from nauticom:

(reason: 550 5.7.1 ... Mail from ##.###.##.## is banned due to spam. Call Nauticom Internet Services at 724-933-9853 if you believe you have recieved this message in error.)

Me: I shrug and try a different email account.
Nauticom: You are spamming. Stop it.
x2

Me: I try a different email account for my contact.
Nauticom: You are spamming. Stop it.
x2

Me: I call my contact. We agree that I will fax her the information. I get off the phone and realize I'm out of ink. I give up and move on to a completely unrelated project. Emailing a friend of mine about an update to a website.
Nauticom: You are spamming. Stop it.
Ah, the friend is on nauticom. Crap.

Me: I email my hubby and ask him to try emailing the friend from a different account. I hear back from him that it went through fine. Ah-ha! It's something to do with my accounts then. I log into my old, dusty dsl-provider email account and try sending from there. While I'm waiting, I dig up information from Nauticom on spam filtering. I email them to find out why I'm boucing. I mistakenly send it from one of my other accounts.
Nauticom: You are spamming. Stop it.

Me: Ack! Ack! Ack! I refuse to call you people. I get back on old dusty dsl-provider account and send them the same message with little thumbtack comment at the end about how contacting support actually bounced as spam.
Nauticom:Standard "thank you for contact support" email.

Epilogue: The support email comes in to my mail account as spam and is quarentined into my junk folder.

Instead of worrying about spam filtering, I suggest we cane spammers.