--- title: "Everything You need to know about Pre-Warmed Inventory!" description: "Everything You need to know about Pre-Warmed Inventory!" url: https://help.inboxkit.com/en/articles/36-everything-you-need-to-know-about-pre-warmed-inventory collection: "Prewarm Inventory" updated: 2026-11-01 language: en --- # Everything You need to know about Pre-Warmed Inventory! Everything You need to know about Pre-Warmed Inventory! Pre-Warmed mailboxes are one of the fastest ways to start sending outreach with strong deliverability from Day 1. Instead of waiting weeks for a new mailbox to warm up, these mailboxes come fully pre-warmed, reputation-boosted, and ready to send. This section explains what Pre-Warmed Inventory means, how it works, and what you must know before purchasing. * * * ## **What Are Pre-Warmed Mailboxes?** Pre-warmed mailboxes are **Google Workspace or Microsoft 365 mailboxes** that InboxKit has already warmed for **4–8 weeks** using our internal warm-up infrastructure. This means: - They have already built positive sender reputation - They have stable inboxing performance - They can send outreach immediately - No warm-up delay - No need to wait for ramp-up cycles These mailboxes are ideal for teams who want to start sending at full capacity without going through the initial warm-up period. * * * ## **How Are Pre-Warmed Mailboxes Different from Normal Mailboxes?** ### **Normal Mailboxes** A standard mailbox (new mailbox) is created fresh and needs: - 21–28 days of warm-up - Gradual daily sending increases - Stabilizing domain + mailbox reputation - A ramp-up phase before using full sending limits ### **Pre-Warmed Mailboxes** A pre-warmed mailbox already has: - 4–8 weeks of warm-up completed - Consistent positive sending reputation - Higher inbox placement reliability - Ability to start campaigns immediately **In short:** Normal mailboxes = need warm-up Pre-warmed mailboxes = warm-up already done * * * ## **Important: Username Changes Reset Warm-Up** When you purchase a pre-warmed mailbox, the mailbox is already warm **with the existing username**. If you change the username (example: from [_john@domain.com_](mailto:john@domain.com) to [_sales@domain.com_](mailto:sales@domain.com)): - You are technically creating a **new mailbox identity** - Warm-up history no longer matches the new username - Mailbox reputation resets - You will need a **new warm-up cycle** So, **only change the username if it is absolutely required.** If you need a fixed username format, we recommend: - Buying fresh mailboxes instead, and warming them normally - Or keeping pre-warmed mailboxes as-is without renaming * * * ## **Why Pre-Warmed Inventory Is Valuable** Pre-warm inventory is ideal for: - Teams that need to start campaigns immediately - Agencies running large-volume outreach - Users who don't want to wait 3–4 weeks for standard warm-up - Anyone who needs stable deliverability from Day 1 You get: - Faster sending - Higher trust score - Better inboxing - Zero ramp-up delays * * * ## **Quick Summary**

Feature	Normal Mailbox	Pre-Warmed Mailbox
Warm-up required	Yes	No
Start sending immediately	No	Yes
3–4 week warm-up included	❌	✅
Username change allowed	Yes	Strongly discouraged
Payment type	Subscription / Credits	Credits only
Best for	Long-term	Instant sending

## Related - [How to Buy Prewarmed Domains / Mailboxes?](https://help.inboxkit.com/en/articles/12-how-to-buy-prewarmed-domains-mailboxes.md)