How to disable or reduce "update available" emails sent to admins

How is your Discourse site hosted @lee7 ? Using our standard install instructions?

The version update emails are sent by a daily Sidekiq job:

There shouldn’t be any reason for the job to run more than once every day. We also have a check to make sure we only notify about a given version once.

All this data is stored in Redis… so my guess would be that you have an unusual Redis configuration?