Some mismatch is expected and normal — the two are measuring slightly different things. Your SMTP provider typically reports whether the message was successfully handed off/delivered, while SubsiMail's open/click tracking measures actual recipient engagement via tracking pixels and link redirects, which depends on images loading and can be affected by things like Apple Mail Privacy Protection pre-fetching opens automatically. For send/delivery/bounce counts, your SMTP provider's numbers are usually more authoritative since that's closer to the actual mail transaction. For opens/clicks specifically, ours is the more relevant number since that's what we're actually designed to track.