Warming up a domain in 2026

The most common deliverability question we get is some version of: my domain is brand new, my list is clean, and my first campaign went to spam. Why?

Because the receiving side has never seen your domain before, and the first thing it saw was fifty thousand messages in an hour. From where Gmail sits, that is what a compromised account looks like. No amount of correct DNS records changes that; authentication proves you are who you say you are, not that you are worth listening to.

Reputation is a history

Mailbox providers score senders on behaviour over time: how many messages bounce, how many get marked as spam, how many get opened, replied to, moved out of the junk folder. A new domain has no history, so it starts with no trust and a very small budget. Every message that behaves well grows the budget a little. Every one that bounces or gets reported shrinks it a lot.

Warmup is the process of spending that budget carefully until it is big enough for your real volume. It is not a trick and it cannot be skipped. It can only be done well or badly.

How Herald does it

• Engaged contacts first. The first week's messages go to the people most likely to open them: recent signups, recent buyers, anyone who has replied to you before. Good behaviour early is worth more than good behaviour later.
• A rising daily cap. Day one sends a few hundred messages. The cap roughly doubles every couple of days as long as the bounce and complaint rates stay low, and holds if they do not.
• Overflow to a warm pool. If you need to send more than the cap allows, the remainder goes out from Herald's shared, established infrastructure instead of being dropped or delayed. Your list gets the message; your domain gets the credit only for what it can safely carry.
• A stop rule. If complaints spike, the ramp pauses and you get an email explaining why. Pushing through a bad day is how a domain ends up on a blocklist.

Three weeks, give or take

For most senders the ramp reaches a hundred thousand messages a day in about three weeks. A cleaner list gets there faster; a list with a lot of old addresses gets there slower, because every bounce costs budget. Either way the schedule is visible in the dashboard, and the delivery log shows every deferral so you can see the receiving side's mood in real time.

If you are moving a domain from another provider, the history comes with it, and warmup is mostly a formality. If the domain is new, start it the day you register it, before you need it. The three weeks pass whether you are watching or not.