Hey Kristen Howard this is called "Marketing pressure" and there is tons of litterature on the topic. This post from Braze for example is a good start.
The most common answer is to monitor your engagement metrics. When Open rates, click rates, and / or unsub rates fall under or rise above a certain level, you know you might have a marketing pressure issue.
As long as they don't, you don't have a mp problem, and you can email people as much as you need to. Despite the occasional rant from unhappy people, you'd get those whether you send daily or yearly emails anyway.
