Tracking is decided the moment you press Send

No. Mailtrack's help center says it is not possible to track emails sent before you started using it, and Streak's support page gives the same answer for any email already sent with or without its tracking image. Every Gmail tracker works this way, ours included. The good news is that the conversation is not lost. The email you send next in that thread can be tracked, and it is usually the better signal anyway.

Why a sent email stays the way it left

An open tracker adds a tiny image to the email at the moment you send it. When the reader's mail app loads that image, the tracker records an open. Click tracking works the same way, by swapping each link for one that records the visit before passing the reader on. Both changes are made to the message itself, so an email that left without them has nothing inside it that can ever report back.

Once it is delivered, the email is a copy sitting in the recipient's mailbox, on their provider's servers. The copy in your Sent folder is yours, and nothing you do to it reaches theirs. Gmail's only grace period is Undo Send: its help page lets you set a send cancellation period of 5, 10, 20 or 30 seconds, during which the message has not gone yet. After that, the email is out of your hands.

The email standard is explicit about this. RFC 5322, which defines the format of an email, says each message carries a unique Message-ID, and that subsequent revisions to the message each receive new message identifiers. A changed email is a new email. Streak points out the mirror image too: you cannot remove tracking from an email that went out with it.

Your second chance is the next email in the thread

Streak's own suggestion is the right one: if the message will be grouped into a conversation, send a reply with tracking on. Reply inside the existing thread rather than starting a fresh email. Gmail's help page on conversations says replies are grouped with the latest email at the bottom, and that a conversation breaks off into a new one when the subject line changes. So keep the subject as it is. Replies also carry headers that point back to the earlier message, which RFC 5322 says replies should have, and that is what keeps your follow-up attached to the original in most mail apps.

Be honest with yourself about what the follow-up's open means. It tells you the follow-up was opened. It does not tell you whether the first email was ever read. In practice that matters less than it sounds, because the person now has the whole conversation in front of them, and the open of the newest message is the one you would act on anyway.

• Make the follow-up worth opening on its own: one new detail and one easy question, so a reader who skipped the first email can still answer.
• Avoid resending the original as a brand new email. It lands in a separate thread, asks the person to read the same thing twice, and splits any reply away from your earlier message.
• Wait as long as you normally would before following up. A missing open on an untracked email is not news, so there is no reason to rush.

Why emails go out untracked in the first place

Untracked sends usually come from one of a few causes, and each has a simple fix.

• The email was sent before the tracker was installed or connected. Those emails stay untracked for good, which is exactly what Mailtrack's help center describes.
• It was sent from a Gmail account the tracker is not connected to. Every account you send from needs its own connection.
• Tracking was switched off for that one email, or paused for everything, and never switched back on.
• It was sent from somewhere the tracker does not run, such as the Gmail app on a phone.

The cheapest habit in email tracking is a glance at the compose window before you press Send.

How Fast Mail Tracker shows what was tracked

Fast Mail Tracker runs inside Gmail in Chrome on a computer. Every compose window gets a small tracking chip next to the Send button that reads On or Off. It starts On, and clicking it switches tracking off for that one email only, so the state is visible at the moment it matters. In your Sent folder, every row gets a mark. A tracked email shows its read state, and an untracked one gets a muted grey mark that says Email not tracked when you hover over it. That tells you which conversations need a tracked follow-up instead of a wait for an open that can never come.

When you reply inside a conversation with tracking on, the tracking image rides on Gmail's own reply. The message keeps Gmail's reply headers, so it stays threaded with the original, and it reports its own opens and clicks from there.

Fast Mail Tracker is in early access while Google's security review completes, so places are limited; to make sure your next email goes out tracked, use the install button below.