Troubleshooting

Why aren't my open rates accurate?

Open tracking relies on a 1x1 pixel, which modern mail clients distort in both directions. Treat opens as a directional signal, not an exact count.

Open tracking works by embedding a 1×1 tracking pixel (a tiny image) in the email. An "open" is recorded when that pixel is fetched. The problem: modern mail clients fetch — or refuse to fetch — that pixel in ways that have little to do with whether a human actually read your message. Opens are inflated by some clients and undercounted by others, so treat the number as directional, not exact.

Use opens to compare campaigns against each other (is this subject line trending up or down?), not as a literal headcount of readers. Clicks are a far more reliable engagement signal.

Why opens get inflated

Apple Mail Privacy Protection (MPP)

When a recipient uses Apple Mail with Mail Privacy Protection enabled, Apple pre-fetches every image — including the tracking pixel — on Apple's servers, for every message, whether or not the user opens it. This both inflates opens (messages register as "opened" that were never read) and obscures them (the fetch comes from an Apple proxy with a generic location/user-agent, so you cannot trust the open's timing or geography). A large share of opens from Apple Mail audiences are MPP artifacts.

Security scanners and link previewers

Corporate mail gateways and antivirus scanners (Mimecast, Proofpoint, Barracuda, Microsoft Defender / "Safe Links", Symantec, Sophos, Trend Micro, and similar) fetch every image and follow every link at delivery time, before any human sees the message. Counting those would log a phantom open (and phantom click) for essentially every message.

Why opens get undercounted

Many recipients have images turned off by default, or read in plain-text/preview panes that never load the pixel. Those people may genuinely read (and even click) your email while never registering an open. So the true number of readers is almost always higher than the open count for image-off audiences.

Gmail clips messages over 102KB

Gmail clips any message larger than 102KB, hiding the tail of the email behind a "View entire message" link. Because the tracking pixel typically sits at the bottom, a clipped message does not register an open unless the recipient expands the full message. Keep your HTML well under 102KB to avoid silently losing opens (and clipped content).

Plain-text-only emails are never tracked

Open tracking depends on the 1×1 pixel, which only exists in an HTML body. An email sent with only a plain-text version has nowhere to put the pixel, so it can never record an open at all — even though the recipient may read it fully.

How MailBlastr filters opens

To keep opens as meaningful as possible, MailBlastr applies two filters before recording an open:

Scanner / prefetch filtering — pixel hits from known corporate scanners and antivirus gateways (Mimecast, Proofpoint, Barracuda, Microsoft "Safe Links" / "Existence Discovery", Defender, Symantec, Forcepoint, Sophos, Trend Micro, BitDefender, and more) are dropped as machine fetches, never humans.
Prefetch window — any hit arriving within 60 seconds of send is discarded as a delivery-time prefetch (including the image proxy caching the pixel on arrival), not a real read.
Webmail image proxies count. Gmail (GoogleImageProxy) and Yahoo (YahooMailProxy) fetch and cache images on their servers only when the message is actually displayed by a human — so, past the prefetch window, a proxy hit is a genuine open signal and is counted. (Earlier behavior that discarded these meant Gmail/Yahoo opens never registered at all.)

No filter can undo Apple Mail Privacy Protection: MPP fetches look like legitimate post-window opens, so audiences heavy on Apple Mail will still show inflated open rates. Lean on clicks and on relative open trends, not absolute open counts.

Tracking can also hurt placement

Open tracking does not affect whether a message is *delivered*, but it can affect *where* it lands. Trackers are heavily associated with marketers and spammers, so inbox providers may treat a tracked message as promotional and file it accordingly. For transactional mail, where inbox placement matters most, consider disabling open tracking entirely.

What to do

Compare open rates between your own campaigns rather than against an absolute target.
Weight click-through and replies more heavily than opens when judging engagement.
Track impact outside the inbox too — page visits, signups, conversions — since email is usually a means to an end.
Disable open tracking on transactional streams to protect placement.
For list hygiene, treat "no opens AND no clicks over many sends" as the unengaged signal — not opens alone.