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Why a new mailbox starts slowly

A mailbox that has never sent mail has no history with the providers that receive it. Here is what that means for your first weeks, and what warmup can and can't do about it.

Providers keep a record of who sends

When your email arrives, the receiving provider decides what to do with it: deliver it, slow it down or send it to spam. To decide, it uses what it already knows about the sender. Google says Gmail keeps track of how much you send, how people react and which limits apply, for each sending domain and each IP address. (An IP address is the number of the server the mail is sent from.)

A new mailbox has no record yet. The provider knows nothing about it, so it watches what you do first. Google warns that a sudden jump in volume, from a sender with no history of large volumes, can bring rate limiting or a drop in reputation. Rate limiting means the provider accepts only part of your emails and asks you to send the rest later.

You can't read your reputation as one number and fix it. Google is retiring the reputation dashboards in Postmaster Tools, its tool for senders, and says reputation is only one of many factors that decide whether your email arrives, and that the data is hard to act on.

What Google advises when you raise your volume

Google's guidelines for senders give the plainest advice on volume:

  • Start with a low volume, sent to people who want your mail, and raise it little by little.
  • Send at a steady rate. Don't send in bursts.
  • The more you send, the more slowly you should raise the volume. Raising it is easier when you send every day than when you send once a week.
  • If you have no history of large volumes, don't suddenly double what you sent before.
  • If emails start to bounce, or the receiving server asks you to try again later, cut the volume until those errors stop. Then climb slowly again.

The page gives no schedule, so there is no number of emails a day that is right for week one. How fast you can climb depends on who you write to and how they react.

What warmup does, and what it can't

Warmup is a way to follow that advice before you have real mail to send. A new mailbox sends a few short emails a day to other mailboxes, gets some answers back and sends a little more each day. That gives it a first stretch of small, steady, rising volume, with some replies in it.

Warmup can't do these things:

  • Fix a bad list. An email to an address that doesn't exist bounces, whatever the mailbox's history.
  • Stand in for permission. Google says not to send to people who didn't sign up for your mail: they might mark it as spam, and then your later emails to them are marked as spam too.
  • Promise a place in the inbox. Only the receiving provider decides where an email goes, and no one outside it can promise the result. We don't.
  • Make a sudden jump safe. When warmup ends, the same advice holds: raise your volume one step at a time.

A plan for the first weeks

None of this is a provider's rule. It is one way to follow the advice above.

  1. Set up the domain's SPF and DMARC records before anything else. They tell receivers the mail really comes from you.
  2. Connect the mailbox and turn warmup on. Let it run for a while before the first campaign.
  3. Start the first campaign small, with a daily limit far below your goal and a list of people who expect to hear from you.
  4. Raise the limit one step at a time. Wait for the replies and bounces from one step before you take the next.
  5. If bounces go up, stop raising the limit. Check the list first, then the message.

What colding does about it

Warmup in colding starts at 10 emails on the first day, adds 1 a day and stops growing at 40. After 14 days of warmup, a mailbox's first campaign day allows up to 20 emails, and each day it sends adds 5 more, up to the mailbox's daily cap. Read how warmup works.

On top of that, a campaign pauses by itself when 5% of its emails bounce or 0.1% are marked as spam over 7 days, and only once 50 emails went out in that time. These are our own limits, not a provider's. They stop a bad list early, and they promise nothing about where your mail lands. Read how campaigns work.

Sources

We read these pages on October 5, 2026. They are in English. If a provider has changed its page since, the provider's page is right and this essay is out of date.

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