All of the below symptoms are telltale signs that a spam filter is clicking on your links:
- unusually high click rate
- clicks by the same recipient (especially from the the same domain) to every single link in your email
- clicks from emails ending in certain domains are much higher than from other domains
- clicks that seem to have come from a bot (lots of clicks recorded within a very short period of time)
- contacts seem to have accessed links directly instead of clicking on a button or link in your email. For example the click report shows links directly as https://abcdomain.com vs "Read more" even though you didn't have https://abcdomain.com as a link in your email.
Some overzealous spam filters click links in emails as they analyze links for potential malicious content.
There is no way to tell apart "real" clicks from clicks by bots.
This issue is relatively rare and only affects organizations with aggressive spam filtering systems.