What is send time optimization (STO)?

Send time optimization (STO) personalizes delivery timing based on individual recipient behavior patterns rather than sending to everyone simultaneously.

STO systems analyze historical engagement data to identify when each recipient typically opens emails. They then schedule delivery to arrive during each person's optimal window.

How it works:

The system tracks when each recipient has opened previous emails. It identifies patterns (always opens at lunch, checks email first thing in morning). It delivers your email to land in the inbox during that window.

Benefits: Higher open rates from reaching people when they are checking email. Reduced inbox competition from better timing.

Limitations: Requires historical data. New subscribers start with defaults. Patterns change over time.

STO automates what manual testing discovers. It applies individual timing optimization at scale.