Email Warmup: What It Is, How Long It Takes and How to Do It Right

Email warmup is a slow, planned increase in how much a new or idle mailbox sends, so providers like Gmail and Outlook see a normal history before your real volume arrives. Most new mailboxes need two to six weeks of it before cold campaigns, and warmup tools such as Warmy automate the ramp by trading email with a network of other inboxes. If you are weighing Warmy specifically, our Warmy review covers what it does, what it costs and where it stops.

Some tool links here are affiliate links (disclosure). Nerdy Joe is an affiliate of Warmy and MailReach, and holds affiliate links only for Instantly and Smartlead. Nerdy Joe is a certified Apollo.io Managed Services Partner and a PlusVibe Certified Silver Partner.

We have not tested Warmy or any warmup tool hands-on for this guide. Vendor facts come from each vendor's own pages as of November 2026, provider rules come from Google, Yahoo and Microsoft, and every source is listed at the end.

What email warmup is

Google's sender guidelines describe the idea without using the word. Gmail tells senders to "Increase volume slowly", send at a consistent rate, "Start with engaged users", and avoid sudden spikes. That is the whole principle, and every warmup method is a way of following it.

There are three things people warm up, and they are often confused:

Cold email teams on Google Workspace or Microsoft 365 send from the provider's shared IPs, so in practice they warm mailboxes and domains, not IPs.

How warmup tools work

A warmup tool connects to your mailbox and sends low-volume messages to other mailboxes in its network. Those mailboxes open the messages, reply to some, and move any that land in spam back to the inbox. Volume rises a little each day.

Warmy describes its version this way: network mailboxes open every email, reply to about 30%, mark messages as Important, and rescue spam-filed messages, while daily volume rises gradually. Warmy says its network has more than 1 million mailboxes, though its own FAQ cites at least 300,000, and it says the network is "mainly Warmy-managed mailboxes, plus a smaller share of accounts belonging to Warmy users."

Warmy also lets you warm with your own templates, choose topics and industries, write in 30+ languages, and set the provider mix. It can warm marketing platforms and transactional services such as Mailchimp, SendGrid and Amazon SES, not only Gmail and Outlook mailboxes, which most cold email warmup tools do not cover.

MailReach takes a different view: it says it does not offer template, industry or language warmup and argues those features do not help; neither vendor has published independent data. Our Warmy vs MailReach comparison puts the two approaches side by side.

How long email warmup takes

No mailbox provider publishes a warmup timeline. The numbers below are vendor and ESP guidance, so read each as that source's recommendation.

Warmy's own pages do not fully agree with each other: its product page says 3 to 4 weeks for a new domain, its help center says at least 2 months, and another help article says new domains usually see improvement within 3 to 6 weeks. Warmy also offers ramp speeds: Slow (4 to 6 weeks), Medium (2 to 4 weeks) and Fast (1 to 2 weeks), and it recommends Slow.

The practical reading: two to four weeks of warmup only for a new domain, then small campaigns with warmup still on.

Manual warmup vs warmup tools

Manual warmup means sending real email to real people who will open and reply: colleagues, partners, existing customers, friends of the business. It follows Google's advice to start with engaged users more literally than any tool can, because the engagement is genuine.

Tool warmup automates the same ramp with a network. It is faster to run across many mailboxes, but the engagement comes from network inboxes, not your buyers.

A sample warmup schedule

The schedule below is illustrative. It is our own blend of the vendor guidance in the table above, not a rule from Google, Microsoft or any tool. Adjust it to your tool's defaults and stop the ramp if bounces or complaints rise.

For reference points: Warmy's high-volume cold outreach article suggests starting at 10 to 20 emails a day during warmup and raising over two to four weeks, and its B2B guide suggests keeping about two warmup emails for every cold email. MailReach says its Autopilot pace reaches about 50 warmup emails a day by day 14, and it recommends no more than 100 cold emails a day per address.

If a mailbox starts bouncing or deferring, Google's advice is to reduce volume until the errors drop, then increase slowly again. Our guide to email bounce rate covers what counts as too high.

Warming Google vs Microsoft accounts

The principle is the same everywhere, but the setup and the provider rules differ.

Google Workspace and Gmail

Google's rules apply to mail sent to personal Gmail accounts. All senders need SPF or DKIM, valid forward and reverse DNS, TLS, and a spam rate in Postmaster Tools below 0.3%.

Senders of 5,000 or more messages a day also need SPF, DKIM and DMARC, alignment, and one-click unsubscribe for marketing and subscribed messages. Google says to keep spam rate below 0.10%.

Connecting to a warmup tool usually means an app password (IMAP and SMTP) for a single mailbox, or admin approval in the Google Admin console for a Workspace domain. Warmy documents both, plus domain-wide delegation for bulk connection of up to 1,000 mailboxes.

Outlook and Microsoft 365

Microsoft requires domains sending more than 5,000 emails a day to Outlook.com consumer addresses to pass SPF and DKIM and publish DMARC at p=none or stronger, aligned with SPF or DKIM. Since May 5, 2025, non-compliant mail is rejected with a 550 5.7.515 error, according to Microsoft.

Microsoft's sender support page says new IPs "typically don't have any reputation built up" and calls the junk complaint rate one of the main drivers of reputation. It also advises against sending to recipients who never read or reply.

Warmy calls Outlook and Yahoo the hardest providers to reach and recommends a provider mix of no less than 25 to 35% per chosen provider for B2B warmup.

Domain warmup and IP warmup, briefly

Domain warmup. A new domain has no history at any provider, so every mailbox on it starts cold. Buy domains a few weeks before you need them, authenticate them fully, and warm several mailboxes on each domain slowly rather than one mailbox fast. Our cold email infrastructure guide covers domain and mailbox setup.

IP warmup. This matters when you send through a dedicated IP, usually on an ESP such as Amazon SES, SendGrid or Mailgun. Amazon says providers are "less likely to accept mail from new IP addresses that have little or no history" and that its automatic warmup runs over 45 days. Microsoft notes that a domain already authenticated under existing SPF records may carry some reputation to a new IP, which can speed up the ramp.

Is automated warmup allowed?

Google's sender guidelines recommend increasing volume slowly to engaged recipients and do not mention warmup tools. Gmail's program policies prohibit automating Gmail in ways that mislead or deceive users. In 2023, GMass said Google required it to shut down its API-based warmup.

Warmy says it is not affected by those API restrictions and that its warmup emails stay inside its own network; its terms make customers responsible for following their email provider's policies. MailReach says Google has not banned warmup and that it follows provider rules. Google has not published a position on warmup networks specifically, so treat automated warmup as a practice Google neither endorses nor explicitly names.

Free vs paid email warmup

Free warmup exists, but it is limited or bundled into something else. As of November 2026:

Warmy's pages conflict on whether its plan volume is shared across mailboxes or the $49 entry price is per mailbox, so confirm mailbox slots in the app before buying. The full Warmy review walks through that pricing question.

When a paid email warmup service is worth it

• You send from a tool without warmup, such as a CRM, a marketing platform or a custom SMTP setup.
• You send B2C or marketing email through an ESP. Warmy covers ESPs and transactional services and offers seed list engagement for real campaigns.
• You want testing and monitoring together. Warmy bundles warmup with placement tests, DMARC monitoring, email verification and Google Postmaster data, per its comparison pages.
• You run few mailboxes and want simple per-mailbox pricing. MailReach is cheaper for 1 to 5 mailboxes; Warmy's own comparison page agrees.

For a ranked comparison of built-in and standalone options, see the best email warmup tools roundup. Run one warmup network per mailbox, not two.

What warmup cannot fix

Warmup is a starting signal. It does not change the things providers weigh most.

• Real complaints. Google's spam rate thresholds apply to reports from real recipients. Warmup engagement comes from network inboxes and does not offset them.
• Bad lists. Invalid addresses bounce whether a mailbox is warm or not. Verify every list first; our roundup of the best email verification tools compares options.
• Broken authentication. Missing or failing SPF, DKIM or DMARC will block mail at Microsoft and Gmail regardless of warmup history.
• Spammy copy and links. Warmy itself says warmup alone does not fix bad addresses, broken authentication or spammy templates.
• Poor targeting. Microsoft advises against sending to people who never read or reply, and Google tells senders not to email people who did not sign up.

Warmup scores also measure the network, not your campaigns. Warmy says its deliverability score is based on warmup emails, and MailReach says its reputation score is not an indicator of whether an address is ready for campaigns. Test real campaign mail with a seed placement test, and if mail is already landing in spam, work through why your emails are going to spam before you add more warmup.

For how warmup, daily health checks and resting mailboxes fit into a full outbound system, see our write-up on mailbox warmup and inbox placement.

Email warmup checklist

• [ ] Domain bought and authenticated: SPF, DKIM and DMARC all pass on a real sent email
• [ ] Warmup running on a slow ramp for at least two weeks before campaigns
• [ ] List verified before the first cold send
• [ ] First campaigns at 10 to 20 a day per mailbox, to best-fit contacts
• [ ] Postmaster Tools verified and spam rate below 0.10%
• [ ] Warmup left on after launch

Rather not build the list yourself?

Warmup is one stage of outbound, next to domains, verified lists, copy and reply handling. Nerdy Joe is owned by Agency Growth Partners (AGP), and AGP builds verified lists and runs outbound for agencies.

If you would rather hand that off, book a call with David.

Bottom line

Email warmup is a slow ramp that gives new mailboxes and domains a normal history, and two to four weeks before campaigns is a sensible default for a new domain. Use the warmup in your sequencer if you have it, add a standalone tool when you need ESP, B2C or testing coverage, and judge results by real bounces, replies and spam rate.

To try a standalone tool, start Warmy's 7-day trial on one mailbox with no card. Our Warmy review explains the plans, the pricing questions and the weaknesses to know first: read the Warmy review.

Disclosure: My relationship with Instantly is that of an independent party. I do not hold any position, nor do I have the power to form binding agreements or act on behalf of Instantly. My earnings are derived from referral compensations provided by Instantly. The views I share are solely mine and should not be seen as official statements, promises, or representations of Instantly, or any related entities or personnel.

Sources

• Gmail Help: Email sender guidelines
• Gmail Help: Gmail Program Policies
• Microsoft Support: Sender support in Outlook.com
• Microsoft Tech Community: Outlook's new requirements for high-volume senders
• Amazon SES: Warming up dedicated IP addresses
• Warmy: Email warm-up
• Warmy: Pricing
• Warmy: Warmy vs MailReach
• Warmy: Warmy vs lemwarm
• Warmy: FAQ
• Warmy: Terms of Service
• Warmy Help: Email sending process
• Warmy Help: How long should I use Warmy
• Warmy Help: When will I see results
• Warmy Help: Warming up for B2B vs B2C
• Warmy Help: Warm-up for high-volume cold outreach
• Warmy Help: Temperature
• Warmy Help: Trial guide
• Warmy Help: Domain-wide delegation
• Warmy Help: The inbox deliverability checker
• Warmy blog: GMass alternative
• GMass: Warmup shutting down
• MailReach: Homepage
• MailReach: Pricing
• MailReach blog: Gmail warmup
• MailReach blog: Email warmup solutions, in-house vs third-party services
• MailReach Help: Getting started after connecting an email account
• MailReach Help: How to get the highest reputation score
• Warmup Inbox: Pricing
• Instantly: Pricing
• Smartlead: Pricing
• PlusVibe: Pricing