Help: spammers flooding my autoresponder
I host an auto-responder that doesn't require a double opt-in. Anybody can come and create an account and they will start receiving our
series of emails.
The problem is that I am being attacked by a persistent group of hackers/spammers that are installing bogus accounts and using proxies to
do their work.
Although I've filtered all their IP addresses and eliminated the bogus email accounts, they still come at me every day! I've thought
about using a CAPTCHA but that will only slow them down, it won't stop them
Is there some way that I can stop this attack, other than using a double opt-in?
I thank you for your help and look forward to your input.