If people click to view the email in their browser, does that mean they cannot read it?

ContentMX Email Deliverability, Knowledge Base

I see in my email reports that people have clicked to view their email in their web browser; why is that? Is that a preference? Are they unable to read the email?

This is just a user preference. It usually means they received the email, but it was convenient to click the first link to view the full email in their browser. Clicks on this link do not necessarily mean people are unable to read the email in their email program (although in some small number of cases that could be true). Sometimes people on an older mobile device or email program might find a better user experience to click the link to read the email.