I'm thinking that I may need to consider creating an "eCommerce Integration Plugin" as I don't see any way to do it with the API, but thought I'd ask....
What I'd like to achieve is to configure Campaign Monitor to call a CMS .aspx page with a customer ID so that the CMS can generate the HTML for the email that is about to be send. That way each email is visually tailored, targeted and personalized with individual products collections. Think # customers = # of segments.
I thinking that I could build a standalone API orientated application piece, but from the API I may end up with 3 million templates in the first week.
It's not really that clear to me exactly what you're hoping to achieve using Campaign Monitor, although you can achieve a callback to your server from Campaign Monitor using our list webhooks.
Hopefully you'll be able to do what you need to using our webhooks.
You can create a draft campaign from the API, and pass in the URL to your CSM .aspx (including the customer ID in the URL) as the 'HtmlUrl' parameter, allowing your CMS to provide the full HTML for the campaign.
This allows your CMS to generate unique HTML for each campaign, but not for each campaign recipient. Does this provide what you need?