Benchmarks / Warmup placement

Does email warmup work?

Based on 850 million+ emails · Smartlead platform data

Warmup emails reach the inbox about 99% of the time on every major provider. Outlook reaches 99.0%, and Gmail and custom servers reach 98.8%. That is about 1 warmup email in 100 missing the inbox, whichever provider you send from.

Warmup inbox placement by provider

Share of warmup emails that reached the inbox, by the provider the mailbox sends from. Built from more than 850 million emails sent through Smartlead.

Provider	Inbox placement	Missed the inbox, per 1,000 warmup emails
Outlook	99.04%	10
Gmail	98.83%	12
Custom servers	98.83%	12

What the data shows

Warmup lands. On every provider, about 99 in 100 warmup emails reach the inbox.

The providers are almost identical. Outlook leads at 99.04%, only 0.21 points ahead of Gmail and custom servers at 98.83%.

Placement isn't where providers differ. The same providers show a wide gap in replies, with Gmail senders needing 90 contacts per reply against 179 on custom servers.

Warmup is usually short. The average sender warms up for 8 days before cold outreach.

How this compares with common advice

Warmup guides mostly report placement gains for single mailboxes, such as one that describes a mailbox going from 40% to 90% inbox placement after warmup. Most also agree warmup can't fix a bad list, broken authentication or weak copy. This data adds the baseline across providers. Warmup mail itself reaches the inbox about 99% of the time, whichever provider you use.

What this data can't tell you

This is placement for warmup emails, not cold campaigns. Warmup mail isn't cold mail, so cold campaigns won't necessarily land at the same rate. The data also doesn't compare cold campaigns sent with and without warmup, so it can't show how much warmup lifts reply rates.

How to use these benchmarks

Warm up every new mailbox with email warmup before it sends cold outreach. The email warm-up guide covers the setup step by step.
If warmup placement sits well below 99%, check the mailbox setup before launching a campaign.
Set up SPF, DKIM and DMARC first. Verified senders need 108 contacts per reply against 120 for unverified ones.
Test where real campaign emails land with a deliverability test, since warmup placement doesn't show that.
Verify the list before the first send. The median sender bounces at 1.54%.

Frequently asked questions

Does email warmup work?

Warmup emails reach the inbox about 99% of the time on Gmail, Outlook and custom servers alike. The data doesn't compare cold campaigns sent with and without warmup, so it shows that warmup mail lands, not how much warmup lifts replies.

What is a good inbox placement rate?

For warmup emails, about 99%. Outlook reaches 99.0%, and Gmail and custom servers reach 98.8%. If your warmup placement sits well below that, check your authentication and sending setup.

Which provider has the best warmup inbox placement?

Outlook, by a small margin. It reaches 99.04%, against 98.83% for Gmail and custom servers, a gap of 0.21 points.

Methodology

More than 850 million emails sent through Smartlead, using combined, anonymous platform data only. Only senders with at least 500 emails sent in the period are included. Inbox placement is the share of warmup emails that reached the inbox, grouped by the provider the mailbox sends from.