Plugin for multiple emails / auto responder?

Hi all

I’ve been looking in the plugins directory but have not found anything, am just wondering if anyone else has found something that might suit…

I am looking for the ability to have someone run a search for types of vendors, who will be a custom post type with a contact email address. I’d love to be able to have the form mail all vendors in the search results, informing them of the email address of the person performing the search. This would be straightforward, but I’m thinking about the implications for server load and therefore need a plugin that can throttle the sending of emails to multiple recipients.

Has anyone used such a plugin, or produced a hack that might make this task feasible?

Many thanks in advance

John