Autoresponder mailing list auto-reply script needed

I am extremely frustrated by autoresponders out there. None seem to actually work when an email is sent to a certain email address!! This is what I require: A script that I can upload to my website that will automatically add email addresses to a mailing list when those email addresses send an email to a particular email of mine. The mailing list would then have the options of sending periodic emails (say instantly, in 2 days, then in 6 days, etc). I intend to use this for my eBay business in this way: 1. Someone buys something, pays via paypal from customer-email to my-email 2. The script automatically adds this email to the mailing list 3. The mailing list automatically sends an email (thanks 4 buying, etc), as well as a few follow up emails I would want the option for the customer to opt-out at any time, as well as being able to opt-in to a more frequent newsletter (eg, weekly). This more frequent newsletter could also run via this script, although, it is not essential (I can set one of those up myself). Preferably, the email the PayPal payment is sent to is @[login to view URL] due to the massive quota. Gmail uses SSL. I have tried a heap of the free scripts, as well as a few others that were cheap, all of which were great except there was no way for emails to be added simply via those emails sending an email to my email. I dont mind if you just edit an existing free script or something like that, as long as its allowed by the terms of service etc :). If I have been unclear anywhere here please let me know