Quick Summary:
Messages are spaced based on when the previous message was actually sent, and they go out during your configured sending window. Messages send one at a time per email account, spaced a few minutes apart to protect deliverability.
When you pause a campaign, the gap timers keep running — so when you resume, any messages that became due during the pause will queue up and send gradually during your next sending window.
How Message Scheduling Works
Each contact receives messages on a schedule based on the gap you set between steps. The gap is measured from when the previous message was actually sent — so if message 1 goes out Monday and the gap is 3 days, message 2 becomes eligible on Thursday.
Messages go out during your configured sending days and hours, typically as soon as they're eligible. Occasionally a message may be slightly delayed if your email account is near its sending limit or there's a high volume of messages in the queue.
To keep your sending looking natural and protect your email reputation, messages are sent one at a time per email account, spaced a few minutes apart.
Pausing and resuming
You can pause a campaign anytime from the Campaign Dashboard. While paused, no messages are sent — but the gap timers keep running in the background. When you resume, any messages that became "due" during the pause will begin sending within your next sending window, going out one at a time per account. After those catch up, your campaign continues on its normal schedule.
Example
You have 30 contacts who each received message 1, with a 3-day gap before message 2. You pause on day 2 and resume on day 10. All 30 now have message 2 ready, so the system works through them over the next couple of hours — sending one every few minutes per account — rather than all at once.