Quiet hours
A configured time window during which email sends are suppressed to respect recipient timezone preferences.
Quiet hours are a configured time window during which a sender suppresses marketing email sends in respect of recipient time zones — typically nights and weekends. The most common policy is no sends between 9 PM and 7 AM local time, no sends on weekends. Quiet hours are enforced per-recipient based on their stored timezone, not server time.
The case for quiet hours is engagement: emails delivered at 3 AM local time wait until morning before being seen, by which point they've been pushed down the inbox by other arrivals. Emails sent at 10 AM Tuesday in the recipient's timezone get opened in minutes. The lift from timezone-aware send timing is meaningful — typically 5-15% open-rate improvement for global lists.
The operational requirement is collecting timezone at signup (modern signup forms detect it via JavaScript) or inferring from IP/locale data. Most ESPs support both timezone-aware sends and quiet-hours configuration. The hardest part isn't enforcement, it's actually having the data. Lists that grew before timezone collection became standard often lack the field entirely.