Here's the gist of the project:
Customer Joe comes to our website and uses search to browse our inventory for A Cool Resort for sale. Joe doesn't find what he's looking for, so he signs up to recieve an email alert when new inventory for sale at A Cool Resort. Then, on days we upload new inventory, an email is generated and sent to him to provide the basic information and encourage him to click through to the site. Same goes for Customer Jane, who is searching for Rad Resort for rent, or Customer Steve who wants to find something for sale or rent in Florida.
This means that we would need unique content emails for the following possible combinations:
Inventory at a resort for sale and rent
Inventory at a resort for sale
Inventory at a resort for rent
Inventory at a location (city, state, country) for sale and rent
Inventory at a location (city, state, country) for sale
Inventory at a location (city, state, country) for rent
It would be very simple for us to generate RSS feeds for each of these items, and probably simple enough to tie that feed to a customer email address to pass to whatever is creating and sending the emails.
So far I've been confronted with the following scenario when proposing this configuration to different ESPs. "Yes we do RSS feed based emails, but you would literally have to manually set up each mailing list for each RSS feed as well as the signup, welcome, and template emails for each." Holy manual labor, Batman!
(To make matters more complicated, someone said "well shouldn't someone be able to sign up to get a few different searches in a single email instead of sending them a bunch of different ones for each possible place they want to check?" UHHHHGH I hate how right they are.)
At this point I don't know what's more daunting, the idea of setting up by hand every single list for every single inventory configuration someone could request, or trying to build a stable, compliant email system with competent reporting in house.
(If you saw this a second ago and you're confused, here's what's up: I signed in with an ancient account that was associated with somebody who doesn't work here anymore. All better now.)
Rather than saying all of the functions you described would need to be manually done, I'd say they would have to be done through programming and development mostly in your application.
Our service will allow you to create lists, sign up customers on lists based on their interests, generate emails on your own systems from RSS feeds, and create an email using the content you've generated, and schedule them to be sent to lists (all though API requests). These functions are all accomplished by API Request. All of the logic needed to determine how and when to make those requests rests on your application. Accomplishing what you want to do would largely be a function of including all of the programming, list, and email content management in your application. Our systems automate management of opt-outs to make sure you won't mail to them, and some basic email results reporting.
I think some workable variation of what you're attempting could be desgned to work with our systems through our API. We're happy to offer support for any valid and reasonable use of our API, although the logic and programming would be up to you or your developers.
I hope this information is helpful to you. It may seem daunting to implement your plan, but you're starting with the advantage of knowing in detail what you're trying to accomplish.