I am planning a web-application for voting in closed groups, such as clubs or parties. It should work as follows:

• The club manager uploads a CSV file with the names and emails of the club members.
• The webapp sends each member an email with a unique URL for one-time voting.
• Each member can click the unique URL to vote.
• After the voting deadline, the webapp computes the results and sends them to the club manager (the votes are not secret - the manager may need to know which member sent which vote).

My main concern is that sending many emails to the club members might be considered as spam. I read this other question about how to not be considered a spammer, but that question considers promotional emails. In that case, the best solution is to use a mailing-list handling service such as MailChimp. But for my application it is not a good solution, because:

• My app needs to send a unique voting-link, automatically generated by the webapp, in order to track the voting and associate them with the voters (and to prevent multiple voting by the same person).
• My app typically sends one-time emails - I do not need a service for periodic emailing to a list.

What is a right way to send the voting links from this application?