Optimal Send Time
Send emails at the best time for each contact
Optimal Send Time
Mailnaptic's Send Time Optimization (STO) analyzes each contact's historical engagement patterns to determine the best time to deliver your email. Instead of sending to everyone at once, STO staggers delivery so each recipient receives the email when they are most likely to open it.
How Send Time Optimization Works
STO builds an individual engagement profile for each contact by analyzing:
- Open timestamps — The specific hours and days when the contact has historically opened emails.
- Click timestamps — When they tend to click, which may differ from when they open.
- Timezone — If known, the contact's local timezone ensures sends align with their day, not yours.
- Recency weighting — Recent behavior is weighted more heavily than older patterns to account for changing habits.
For contacts without enough engagement history (new subscribers or inactive contacts), Mailnaptic uses your organization's aggregate optimal time as a fallback.
Enabling STO for a Campaign
In the campaign builder's scheduling step, select Send Time Optimization instead of a fixed send time. You will need to choose a delivery window — the span of time over which emails will be staggered. Available windows are:
- 12 hours — Best for time-sensitive content that still benefits from per-contact timing.
- 24 hours — The most common choice, allowing a full day for optimal delivery.
- 48 hours — Maximum flexibility for non-urgent campaigns where engagement matters most.
What to Expect
When STO is active, your campaign status will show "Sending" for the duration of the delivery window. Emails trickle out throughout the window as each contact's optimal time arrives. Open rates typically improve by 5–15% compared to fixed-time sends, with the greatest improvement seen in audiences spanning multiple timezones.
STO and Automations
For automation emails, STO works slightly differently. Instead of a delivery window, each automation email can have a delay until optimal time setting. When a contact triggers an automation step, the email is held until the next occurrence of their optimal send hour — up to a maximum of 24 hours. If no optimal time is known, the email sends immediately.
Viewing STO Results
After a campaign completes, the campaign detail page includes an STO performance section showing:
- The distribution of send times across the delivery window.
- Open rates by delivery hour so you can see which times performed best.
- A comparison of STO performance versus your organization's average for fixed-time sends.
Best Practices
STO works best with audiences of 1,000 or more contacts and when your subscribers have diverse geographic locations. For small, single-timezone audiences, a well-chosen fixed send time may perform equally well. Avoid using STO for truly time-sensitive announcements where all recipients must receive the email simultaneously.