it just pisses me off to see a bunch of emails come in and then find out that its the same bloody mailing! If I am not going to click your ad the first time sending it to me 2 or 3 more times will not help! I have numerous emails coming into my inbox but it blows me away to see people not remove duplicates. Even if you sign up to a newsletter or service countless times using the same email address, you should only be recieving 1 notice per send.
My favorite spams are the ones from main stream companies that tell you that your site can be better optimized for search engine placement.
Oh reeeeaaalllllyyyyy......I actually took the time and phoned one of these companies and grilled them with questions re. link popularity, meta structure, changes at google etc...they weren't even in the league!
If you have a list, make sure you know a little about it! Marketing 101.
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