Deliver a scheduled campaign within a set window of each contact's own day
Send each recipient at a good time in their own timezone, not one shared time for everyone.
A normal scheduled campaign fires at a single moment for the whole audience. If your contacts are spread across timezones, that means most of them get the email at an off-hour. Recipient local-time sending fixes that: you pick a window of the day (for example 9:00 to 11:00), and each contact is sent within that window in their own timezone. Someone in London and someone in Los Angeles both receive it mid-morning their time.
Set it in the Review step when you schedule the campaign.
The start date you choose is when sending begins. From there, each contact is queued for the next time their local window opens, spread across the window so they do not all send in the same minute.
It is read from the contact's company.
Each contact’s timezone is taken from the company they belong to. Set a company’s timezone on its record so its people send at the right local hour. Any contact with no timezone on file is sent using the fallback timezone you chose when scheduling, so nobody is ever dropped.
A few details worth keeping in mind.