A brand new SMTP server or a fresh provider account has no sending reputation. Blast 20,000 emails through it on day one and inbox providers will treat you as a spammer. Warmup ramps it up gradually, and the queue does all the work.
Switching it on:
- Go to Delivery, then Sending, then the Send Rotation and Warmup panel.
- On the connection's row, tick Warm up.
- Pick a pace: Conservative (50 emails on day one, growing 1.5x daily), Standard (100 on day one, doubling daily), Fast (500 on day one, doubling daily), or Custom with your own starting cap and daily growth.
- Save. The row now shows where it is, for example: Warming up: day 3, today's cap 400.
Now send normally. Queue your 20,000-email broadcast to everyone, today. Each day the queue sends up to the cap, and the rest waits politely and continues the next day. Nothing is failed, nothing is lost, and nothing sneaks out through wp_mail. On the Standard pace a 20,000 send completes in about 8 days: 100, then 200, 400, 800, 1600 and so on.
Details worth knowing:
- The cap never exceeds the connection's own daily limit, and re-saving other settings never restarts a ramp in progress.
- When warmup reaches the daily limit, the row says Warmup complete and the daily limit takes over.
- Warmup also works with rotation: a warming connection takes its small share while your established connections carry the rest.
- If your server is already warm and you just want a ceiling, set a Daily limit on the connection instead. The queue waits the same way when it is reached.