Send when subscribers are most likely to open

A freelance graphic designer sends her monthly newsletter to past clients at 9am sharp every time, because that felt like a sensible business hour to pick when she started — except a fair few of her clients are night owls who check email properly around 10pm, well after her newsletter has already scrolled past a dozen other messages sitting above it in their inbox by the time they finally look.

Send time optimization looks at each contact's own past open-time history and schedules that contact's copy of the campaign to land during their personal high-engagement window instead, within a range the designer sets. A contact with no history yet — someone brand new to the list — falls back to a sensible default time rather than being left unscheduled or guessed at randomly.

Splitting one campaign into many individually timed sends multiplies the number of scheduled jobs behind the scenes — a list of a few hundred contacts becomes a few hundred separate dispatches instead of one. Every dispatch still has to run through a global suppression check at the moment it fires, not only when the campaign was first queued, because a contact could unsubscribe hours after the campaign was scheduled but before their personal staggered slot arrives. Optimising for open time cannot weaken that safeguard for even one recipient in the stagger.

This feature reads open-time history from a tracking pixel, and open tracking has become a genuinely unreliable signal — Apple Mail Privacy Protection and similar features now pre-fetch images for a meaningful share of recipients, registering an 'open' the moment the email arrives rather than when a person actually looks at it. A contact's computed best window is only as accurate as the underlying open data, and for a recipient whose mail client pre-fetches aggressively, that window may reflect delivery timing more than genuine reading behaviour.

A new contact's fallback hour is a reasonable default, not a personalised choice, and stays that way until enough real open history accumulates to compute something better — there is no shortcut beyond the contact actually opening a few emails over time. A business expecting immediate personalisation for every contact from day one will find the newest subscribers on any list are, quite reasonably, sent at the same default hour for a while, which is expected behaviour, not a gap.