Send-Time Optimisation
Email MarketingAlso: STO · Optimal Send Time
Quick definition
Send-time optimisation (STO) is a feature in email platforms that delivers a campaign to each subscriber at the time they personally tend to open email, rather than sending the whole list at once. It relies on machine learning models trained on a contact's past open and click behaviour.
How it varies across Australia
Uplift from send-time optimisation varies by list size and industry, and tends to be largest for lists with long engagement histories and least useful for new or small lists with little behavioural data to learn from. Treat any vendor uplift claim as a starting hypothesis, not a guarantee.
See retention and loyalty benchmarks across Australian industries →What it actually means
Every subscriber has a rhythm. Some check email first thing on the train, some clear their inbox at lunch, some only open anything after nine at night. Send-time optimisation (STO) tries to work out that rhythm for each contact individually and time delivery to match it, instead of blasting the whole segmentation list at 9am because that's when the marketing calendar says to.
The mechanism is usually a simple machine learning model sitting on top of your email platform. It looks at when a contact has opened or clicked in the past, builds a rough profile of their active hours, and schedules their copy of the campaign accordingly. Klaviyo, Mailchimp and most enterprise ESPs offer some version of this.
It's a genuinely useful lever, but a limited one. STO changes when the email lands. It does nothing for subject line quality, list segmentation, or whether the offer inside is worth opening at all. Businesses chasing a stalled open rate often reach for STO first because it's a toggle, not a strategy. It rarely fixes what's actually broken.
Send-time optimisation doesn't fix a bad email. It just makes sure the wrong email arrives at the right time.
How it shows up
STO shows up as a setting inside your email service provider (ESP), often labelled 'smart send time' or 'send time optimisation' at the campaign scheduling step. Once enabled, the same campaign goes out at different literal times across your list, visible in send logs even though the content is identical.
The effect shows up in your open rate and click-through rate trend lines over several campaigns, not in any single send. A one-off comparison against a fixed send time tells you very little because day-of-week and content quality both move the number too.
The Australian context
Australia's time zone spread across the east coast, Northern Territory and Western Australia means a single fixed send time can miss a meaningful chunk of a national list by several hours. A campaign scheduled for 9am AEST lands at 6am in Perth, well before most people check their phone. STO handles this automatically without a marketer needing to build separate segments per time zone, which makes it more valuable for Australian lists than for single-time-zone markets like the United Kingdom.
Where people get this wrong
Related terms
Common questions
Does send-time optimisation actually improve open rates?
Often, but not always. It tends to help most on lists with long engagement histories where the model has plenty of data to learn from. On small or new lists it has little to work with and the effect is usually negligible.
Which email platforms offer send-time optimisation?
Most major email service providers (ESPs) including Klaviyo, Mailchimp, HubSpot and Salesforce Marketing Cloud offer some form of it, often under names like 'smart send time' or 'send time AI'. Availability and sophistication vary by pricing tier.
Should I use send-time optimisation for every campaign?
No. Use it for regular newsletters and evergreen campaigns where timing flexibility doesn't matter. Avoid it for time-bound campaigns like flash sales or event reminders where every recipient needs the email before a fixed deadline.
How is send-time optimisation different from send-time testing?
Send-time optimisation personalises delivery time per contact automatically using their behaviour. Send-time testing, sometimes called A/B testing on time, sends to two groups at different fixed times and compares results. Testing finds a good time for the whole list. Optimisation finds a time for each person.
Debrief
Get the next one
No spam. No fluff. Just the next article, straight to your inbox.
Keep exploring
About New Rebellion
New Rebellion is a marketing intelligence consultancy. We build tools, score Australian businesses on how their marketing actually performs, and publish Debrief every day. This dictionary is part of how we work in the open.
How we think →