Why we don't do warm-up.
Warm-up networks now carry real risk. What Google and Microsoft look at instead, and what to do.
Most cold email tools sell warm-up. We don't, on purpose. Here is why, and what works instead.
What warm-up tools do
Warm-up tools put your mailbox in a pool with thousands of others. The mailboxes email each other. Software opens those emails, replies to them, and marks them "not spam". The aim is to make Google and Microsoft think people love your emails.
Why it can hurt you now
- Google has acted against it. In January 2023, Google told GMass to shut down its warm-up feature or lose access to Gmail. GMass shut it down on 31 January 2023, saying Google now treats warm-up as a terms-of-service violation.
- There is a blocklist for it. In September 2026, Validity launched the Heatwave blocklist. It lists over 1.2 million domains for artificial warming and shares the list with Proofpoint, Spamhaus and Comcast. A warming listing is permanent.
- The numbers can mislead. Warm-up tools measure inbox placement inside their own pool. Users have reported a perfect warm-up score while independent tests put their mail in Gmail spam.
- Experts are turning against it. Deliverability specialists report domains with a worse reputation after warm-up than before.
What Google and Microsoft actually look at
Microsoft weighs the reputation of the sending servers and your domain, and is the hardest inbox to reach. New domains start with low trust, so a slow, steady start matters most.
Google is about compliance. Set up SPF, DKIM and DMARC. Let people unsubscribe in one click. Keep spam reports under 0.1%, and never above 0.3%. Mail that doesn't comply can be rejected outright.
How Google learns about you
As GMass explains: while Google gets to know you, it tests your campaigns by sending some messages to the inbox and some to spam. If the inbox group opens, clicks and replies, your next emails go to more inboxes. If the spam group marks you "not spam", your next emails go to more inboxes too.
So start with small, targeted groups, then grow. In GMass's words: "be your own warmup system".
What to do instead
- Add a few of your own addresses to your first campaigns, such as your personal Gmail or Outlook. Use addresses on a different domain from your sending mailbox: mail inside one domain never passes the spam filter.
- When they arrive, open them, click a link and reply.
- If one landed in spam, mark it "Not spam", then reply.
- Keep the slow start on. Each new mailbox starts at 10 emails a day, then 20, then 30 over three weeks.
- Check your list and fix your DNS. We do both for you: every upload is checked, and every domain gets plain fix steps.
Real people, real replies. That is what builds trust. There is no shortcut.