SMTP warmup: How many emails a day your new server can send

Microsoft cuts a new tenant with one license to 1,000 outside recipients a day. That lasts 30 days.

Google Workspace Help lists 2,000 messages a day for a paid user.

On your own server or IP, replies from Gmail and Outlook set the pace. Start at 5% of the volume you want.

What this page covers

What you need

Publish the SPF, DKIM and DMARC records Gmail, Yahoo and Outlook.com require before day 1. Pick a target number of emails a day.

Keep a way to read replies from Gmail and Outlook, like your mail log.

Which setups it covers

This page covers a Google Workspace user, a Microsoft 365 tenant and your own IP. A shared IP at a provider is not covered.

Google states: "Sender requirements and Google enforcement apply only when sending email to personal Gmail accounts."

Its bulk sender requirements start at 5,000 or more messages a day to Gmail accounts. New domains face an accelerated enforcement timetable.

Daily limits by setup

This table lists the published limit for each setup.

Every number in this table is a ceiling. Stay below the row that applies to you.

Warm up a Google Workspace user

Google counts the limit for each user over a rolling 24 hours.

Steps:

1. Find out whether the user is on a paid or a trial account.

2. Read that account type's row in the table above.

3. Set a daily number below that row, using the plan further down.

Trial limits stay until the domain has paid at least $100 USD. Google says the rise can take up to 75 days after that.

One user stops at 2,000. To send 3,000 messages a day, you need 2 users.

Confirm: Send a test message to a personal Gmail address. In the message headers, Authentication-Results shows spf=pass, dkim=pass and dmarc=pass.

Warm up a Microsoft 365 tenant

Microsoft counts outside recipients for the whole tenant. Every mailbox shares one daily limit.

Message Center post MC1454397, updated 29 September 2026, lowers the limit for new tenants. Days 1 to 30 get 10% of the standard limit. Days 31 to 60 get 25%.

After day 60, the full limit applies. Your tenant may not have the cut yet.

The standard limit is 500 × licenses^0.7 + 9500. For 1 license, that is 10,000. Then 10% of 10,000 is 1,000, and 25% is 2,500.

It also cuts the trial tenant limit from 5,000 to 500 outside recipients per day. Microsoft Learn still lists 5,000 for trial organizations.

Steps:

1. Count the licenses in the tenant.

2. Find your row in the limits table for the tenant's age.

3. Set one daily number for all mailboxes together, below that row.

4. Open the Tenant Outbound External Recipients report in the Exchange admin center.

Confirm: The report shows your tenant's real limit. Use that number if it differs from this page.

Each mailbox using SMTP AUTH has its own cap. Microsoft Learn lists 3 connections at once, 30 messages a minute and 10,000 recipients a day.

Message Center post MC786329 covers Basic Authentication for SMTP AUTH. It goes off by default for existing tenants at the end of December 2026.

Warm up your own server or IP

Gmail and Outlook give you no row to read here. Their replies tell you the pace.

Steps:

1. Set the reverse DNS (PTR) record for the sending IP.

2. Make the name in that record resolve back to the same IP.

3. Publish SPF, DKIM and DMARC for the sending domain.

4. Turn on TLS for connections to other mail servers.

5. Confirm that outbound port 25 works from the host.

6. Send the first day's number from the plan.

Google Cloud blocks outbound port 25 to destinations outside your VPC network. Google Cloud says some projects lack this block. Ports 587 and 465 have no restriction.

Confirm: Gmail returns none of 4.7.23, 4.7.27, 4.7.29, 4.7.30, 4.7.31 or 4.7.32 for that day.

Replies that tell you to slow down

Gmail has ramped up enforcement since November 2025, with temporary and permanent rejections. Any code in this table makes that day not clean.

The Microsoft 365 limit replies are listed under the fixes below. They also make a day not clean.

Two fixes take time to show:

• The Microsoft delist portal can take up to 24 hours or longer.

• For 5.7.511, Microsoft replies within 48 hours.

Build your plan

Published schedules disagree. TrulyInbox estimates about 23 days to reach 50 emails a day. BounceZero lists 4,000 on day 14. Build your own plan from the limits above.

Rules for each day

1. Pick your target. It stays at or under the row that applies to you.

2. Send 5% of the target on day 1. The 5% is this page's own choice. No provider sets it.

3. After each clean day, add the same amount again. A clean day has no Gmail 4.7 or 5.7 codes and no Outlook block codes.

4. After a day that is not clean, go back to the last clean day's number. Hold it for one clean day.

5. Stop raising when you reach the target.

Example plan

Say your target is 300 outside recipients a day. The tenant is new, with one license, so the limit is 1,000 and 300 fits.

• 5% of 300 is 15, so day 1 sends 15.

• Each clean day adds 15.

• Day 5 sends 75, day 10 sends 150 and day 15 sends 225.

• 300 divided by 15 is 20, so the target arrives on day 20.

Fix the four failures people hit first

Gmail returns a 4.7 code

Find the code in the table above and fix the record it names. For how Gmail words its blocks, read what a message blocked notice in Gmail says. For temporary 4xx replies in general, read SMTP error 421.

Outlook returns S3150 or 5.7.606 to 649

Outlook returns one of these replies when the sending IP is blocked:

550 5.7.1 Unfortunately, messages from [IP address] weren't sent. Please contact your Internet service provider since part of their network is on our block list (S3150).

550 5.7.606-649 Access denied, banned sending IP [Source IP address]: To request removal from this list please visit https://sender.office.com/ and follow the directions. For more information, see Email non-delivery reports in Exchange Online.

The first line is from a Microsoft Q&A post with the IP replaced. A Microsoft moderator replied the next day. The reply sent the poster to the delist portal at sender.office.com. Microsoft Q&A shows the thread, dated 16 February 2026.

Fix it:

1. Stop sending to Outlook, Hotmail, and Microsoft 365 addresses.

2. Enter the blocked IP and the address that received the bounce at the portal.

3. Open the confirmation email and select the link.

4. Select Delist IP.

Microsoft Learn lists these steps. It sends a code 5.7.511 to delist@microsoft.com, and the portal does not apply to it.

Microsoft 365 returns 5.7.233

550 5.7.233 Your message can't be sent because your tenant exceeded its daily limit for sending email to external recipients (tenant external recipient rate limit).

All users in the tenant are blocked from sending to outside recipients. The limit counts recipients, so one message to a long list uses many of them.

A mailbox using SMTP AUTH is throttled

432 4.3.2 Concurrent connections limit exceeded.

554 5.2.0 STOREDRV.Submission.Exception:SubmissionQuotaExceededException

The first reply comes from more than 3 connections open at once. The second comes from passing 10,000 recipients in a day.

Ramping a send-only SMTP with no inbox to watch? How TrueEmailer helps

A send-only SMTP can push mail out, but it cannot show you the replies that tell you to slow down. You need an inbox and a daily plan, and the plan above needs both.

This page is published by TrueEmailer, which sells an email platform. TrueEmailer lists an AI Warmup Agent and a Unified Inbox for replies.

It verifies each connected domain with SPF, DKIM, and DMARC. You connect an SMTP or a sender domain to start sending.

For a side-by-side view, read email warm-up vs. pre-warmed SMTPs.

Warmups depend on the plan. Kickstart and Basic include 0 warmups. Starter includes 2 and Pro includes 5.

FAQ

How long does SMTP warmup take?

The example plan takes 20 days to reach 300 emails a day. A new Microsoft 365 tenant has a lower limit for its first 60 days.

Do I need to warm up on Google Workspace or Microsoft 365?

Yes. A Workspace trial user has 500 messages a day. A new Microsoft 365 tenant has 10% of its standard limit for 30 days.

How do I know it is warmed up?

Call it warmed up after 7 clean days at your target. That rule is this page's own, not a rule from Google or Microsoft.

Can I warm up without a paid tool?

Yes. The plan above needs a daily number and your mail log. For the wider picture, read how email warm-up works for cold outreach.

Set your first number

Find your row in the limits table and set your target at or under it. Send 5% of the target on day 1. Raise it only after a clean day.

Google says its limits can change without notice, so read them again before day 1.

Steps verified 12 October 2026 against Google Workspace Help, Microsoft Learn and Google Cloud documentation.