How long does email warmup take?

A new mailbox on a fully authenticated domain needs about 2 weeks of warmup on Google Workspace and 3 on Microsoft 365, followed by a slow ramp. SimpleSend runs that schedule automatically: by default each new mailbox sends at most 10 cold emails a day in its first week of sending and 18 in its second, then moves up to your daily cap (each mailbox's ramp can be changed). Aged domains help, but they are not required. If your tool does not ramp for you, the conservative schedule is three to four weeks of warmup and about six weeks to full volume. Reputation does not transfer between mailboxes, so every new one starts the clock again.

Do I need automated warmup tools?

For multi-inbox cold outbound, automated warmup is the practical option. SimpleSend warms every mailbox you buy in the app automatically and keeps warmup running while you send. With your own mailboxes, a tool like Smartlead, Instantly or Mailreach does the same job. Manual warmup works for a single account but cannot keep up with the daily engagement signals needed to warm several inboxes in parallel.

How do I check my sender reputation?

Use Google Postmaster Tools for Gmail-side reputation and spam rate on domains you manage, Microsoft SNDS if you control your sending IPs, and MXToolbox for blacklist checks across more than 100 blocklists at once. Postmaster needs a DNS record to verify the domain, so set it up before you start warming. For a domain SimpleSend registered and manages for you, contact support to set it up.

Email Warmup and Domain Health Guide

Sending cold email from a brand-new domain or inbox almost always results in spam placement. Inbox providers do not trust senders with no history. This guide explains how to build that history before you launch a campaign, what to monitor while you are sending, and how to keep your reputation clean over time.

Why warmup matters

Gmail, Outlook, and Yahoo Mail build a reputation profile for every domain and sending account they encounter. They track how many emails you send, how many bounce, how many recipients mark your messages as spam, and how many engage positively by opening and replying. A new domain has none of this history, which these systems treat as a risk signal by default.

Warmup is the process of building a positive sending history gradually. Starting at low volume and increasing slowly over several weeks mimics how a real person or business would naturally begin using a new email account.

Skipping warmup creates several problems:

Gmail or Outlook may rate-limit or defer your sends in the first 24 to 48 hours.
Without positive engagement signals, your emails land in spam folders rather than the inbox.
If enough recipients mark early emails as spam, the domain can end up on a blocklist that is difficult to exit.
Reputation damage from a bad start compounds: once you are flagged, recovering takes longer than warming up correctly would have.

Domain warmup vs. inbox warmup

These are related but not the same thing.

Domain warmup refers to building reputation at the domain level. A brand-new domain registered today (getacme.com) has no reputation with any inbox provider. Domain age and sending history are both factored into deliverability decisions by inbox providers.

Inbox warmup refers to building reputation for a specific sending account. Even if you are using a domain that has been registered for six months, a new Gmail or Outlook account created on that domain starts with no sending history of its own.

For individual-account cold outreach, you need both. Aged domains help, but they aren't required: a new domain with SPF, DKIM and DMARC in place works when each mailbox warms for two to three weeks and then ramps up slowly. SimpleSend runs that schedule automatically for every mailbox you buy in the app. If you set up sending in another tool and it doesn't ramp for you, the conservative route is a domain that is 30 to 60 days old and three to four weeks of warmup per inbox, as in the schedule below.

Manual warmup vs. automated warmup tools

Manual warmup

The manual approach involves sending a small number of emails per day to real contacts who will reply, and asking them to move any emails that land in spam to the inbox. This works but it does not scale. You also depend on real people replying consistently, which is hard to maintain over a multi-week warmup period for multiple inboxes simultaneously.

Automated warmup networks

Warmup tools connect pools of real email accounts that automatically send, receive, open, and reply to each other's emails. Adding your inbox to one of these networks means it accumulates positive engagement signals on a schedule you control.

How they work in practice:

You connect your new inbox to the warmup tool.
The tool sends emails from your inbox to other inboxes in the warmup network.
Those inboxes automatically open, reply, and rescue from spam if needed.
The daily volume increases gradually over a preset schedule.

Tools with warmup functionality:

SimpleSend: every mailbox you buy in the app warms automatically, about 2 weeks on Google and 3 on Microsoft, and keeps warming while you send.
SmartLead: warmup built into the platform alongside multi-inbox sending.
Instantly.ai: warmup network included with all plans.
Mailreach: standalone warmup tool, works with any email provider.
Lemwarm: Lemlist's warmup product.
Warmbox: dedicated warmup with inbox health scoring.

Keep warmup running after you start sending.The positive engagement signals from warmup offset some of the negative signals cold outreach can generate. Most senders keep 20 to 40 warmup emails per day running in the background throughout their campaigns, not just during the initial setup period. SimpleSend keeps warmup running on every mailbox for you.

Warmup schedule

The schedule SimpleSend runs for youEach new mailbox warms for about 2 weeks on Google Workspace or 3 weeks on Microsoft 365 before it's marked Ready. Then it ramps on its own: at most 10 cold sends a day in its first week of sending, 18 a day in its second, then your daily limit (25 by default; you can raise it to 40). You can change a mailbox's cold-email ramp-up on its Sending tab; warmup itself keeps running in the background the whole time, and you don't configure it.

The conservative schedule for other tools

If your sending tool doesn't ramp new mailboxes for you, the schedule below is the safe default. It assumes an automated warmup tool and a target of full cold outreach volume by week 6. Some senders move faster depending on domain age, list quality, and inbox provider. When in doubt, go slower.

Week	Warmup volume / day	Real sends / day	Notes
Week 1	10 to 15	0	Warmup only. Do not send any real campaigns.
Week 2	20 to 25	0	Continue building. Check warmup dashboard weekly.
Week 3	30 to 35	0	Verify DNS auth (SPF, DKIM, DMARC) is passing.
Week 4	30 to 40	5 to 10	Run inbox placement test. Start light sends if passing.
Week 5	30 to 40	15 to 25	Scale if no spam placement. Monitor complaint rate closely.
Week 6+	30 to 40	20 to 40	Full volume. Keep warmup running in background.

This clock resets for every new inbox.You cannot transfer reputation from one inbox to another. Each new account you add to your sending rotation needs to complete its own warmup and ramp before being used for campaigns. In SimpleSend, every new mailbox starts its own schedule automatically.

Google Postmaster Tools

Google Postmaster Tools is a free diagnostic dashboard from Google that shows how Gmail is treating your sending domain. It is one of the most useful signals available for monitoring deliverability.

Postmaster is for domains you manage.Google asks you to prove you own the domain by adding a DNS TXT record, so set Postmaster up on domains whose DNS you control. You can't add records yourself to a domain SimpleSend registered and manages for you; if you want Postmaster on one of those, contact support.

Once active, it shows four reputation levels:

High

Strong signals

Your emails are reaching the inbox reliably.

Medium

Decent

Some filtering may be occurring. Watch for changes.

Low

Action needed

Significant spam filtering in effect. Investigate list quality and sending practices.

Bad

Critical

Most mail being blocked or heavily filtered. Immediate action required.

Postmaster also shows your spam rate. Google's email sender guidelines specify that spam rates above 0.10% begin to affect deliverability, and rates above 0.30% trigger bulk filtering. These thresholds are stated directly in Google's sender guidelines, which took effect for bulk senders in February 2024.

Microsoft SNDS

Microsoft's equivalent for Outlook and Hotmail recipients is the Smart Network Data Services (SNDS) portal. It provides complaint rates and spam trap hit data for your sending IPs, so it's useful when you control those IPs (a dedicated IP on a bulk ESP, for example) rather than sending from Google Workspace or Microsoft 365 mailboxes.

Blacklist monitoring

Email blacklists are databases of domains and IP addresses known to send spam. Major inbox providers check these lists before delivering email. Being listed on one of the significant blacklists causes your emails to be blocked or deferred at scale.

The most consequential blacklists:

Spamhaus: the most widely referenced blocklist.
Barracuda BRBL: common in corporate environments.
Microsoft's own blocklist: maintained internally, monitored through SNDS.

To check if your domain or IP is listed: MXToolbox Blacklist Check queries over 100 blocklists at once. Run this check monthly at minimum, or after any period of unexpectedly high bounce rates.

For automated monitoring, HetrixTools can check your IPs and domains on a schedule and alert you when a listing appears.

Inbox placement testing

An inbox placement test sends your email to a set of real seed addresses across multiple providers and tells you exactly where it landed: Primary inbox, Promotions tab, Spam, or not delivered. This is different from simply checking a spam score: it shows actual delivery behavior.

Run a placement test before launching any new sequence, and any time your reply rate drops unexpectedly or your open rate shifts significantly.

GlockApps: detailed placement breakdown by provider (Gmail, Outlook, Yahoo, etc.).
Mail-Tester: free spam score check; useful for a quick sanity check on a new email.
Litmus: placement testing plus rendering previews across email clients.

Maintaining reputation after warmup

Warmup gets you to a healthy starting reputation. These practices keep it there while you are actively sending campaigns.

What SimpleSend does automaticallyIf you send from SimpleSend, most of this is built in. Unsubscribes, hard bounces and "please stop" replies are suppressed across your whole team, out-of-office replies pause the lead, sends spread across your mailboxes, and a mailbox or sequence pauses itself when bounces spike. Poor mailbox health slows or pauses sending until it recovers.

Watch the spam complaint rate closely. Google's published threshold of 0.10% is the point where deliverability effects begin. Above 0.30%, bulk filtering applies. Track this in Postmaster Tools, not just in your sending platform.

Honor unsubscribes immediately. If someone replies asking to be removed, stop emailing them regardless of whether they went through a formal opt-out link.

Maintain consistent sending volume. Sending 30 emails per day for three weeks and then jumping to 500 in a single day triggers spam filters even at technically safe per-account volumes.

Remove hard bounces immediately. An email address that bounces (the address does not exist) should never receive another send.

Rotate sending accounts evenly. For multi-inbox setups, spread your sends across all available inboxes rather than concentrating volume in one or two.

Warmup checklist

Before warming up

Domain is registered, DNS has propagatedAutomatic in SimpleSend
SPF, DKIM, and DMARC records are live (see Email Engine Setup)Automatic in SimpleSend
Google Workspace or Microsoft 365 account is active on the inboxAutomatic in SimpleSend
Warmup tool is connected and configured with a ramp scheduleAutomatic in SimpleSend

During warmup

Warmup is running daily (check the dashboard at least once per week)
No real campaign sends yetAutomatic in SimpleSend
Google Postmaster Tools domain ownership verified and monitoring (domains you manage)

Before launching your first campaign

Inbox placement test passed (landing in Primary inbox)
Google Postmaster shows Medium or High domain reputation (domains you manage)
MXToolbox blacklist check: clean
Bounce removal is configured in sending platformAutomatic in SimpleSend
List verified through NeverBounce or equivalent before upload
Business mailing address and mailbox signatures are set (SimpleSend won't send without them)

Sources & further reading

Email Warmup and Domain Health