cyber advertising

Concerned about the rising cost of newspaper advetising, I have created an email account in the companies name. Does anyone know of a web-based autoresponder? This is a facility which exists in cyberspace, so it is not hosted by any particular computer, like various popular travelling email accounts (eg yahoo, hotmail etc). The difference is that the public can send a "subscibe" email to the list and it will automatically respond by adding them to a list of email addressess to recieve your email, obviously they can also "unsubscribe". Many theatre companies have loyal audiences due to their locality or association and this is a very strong factor in Geraldton, where our advertising will "preach to the converted" as it were. obviously there is no budget, therefore a free service is sought. compatability with older computers and open source software is a bonus, as the entity needs to be maintained by community volunteers. Any sleek geeks out there got any suggestions?