what does warming up an inbox mean?

Warming up an inbox means building its sender reputation gradually before you use it for real outreach. A brand-new mailbox has no history, so Gmail, Outlook and other providers do not know whether to trust it. If it suddenly sends hundreds of cold emails, they treat it like a spammer.

What warmup actually does

• Starts small and ramps up. The inbox sends a few emails a day, then more, so volume grows the way a real person's would.
• Earns positive engagement. Emails are opened, replied to, marked as important and moved out of spam. These are the strongest trust signals inbox providers use.
• Keeps going. Reputation is not a one-off. Steady, healthy activity keeps it high once your campaigns start.

Why it matters for cold email

Inbox providers judge every sender on reputation. Without warmup, a new inbox has none, so even a well-written email can land in spam. With warmup, by the time you start a campaign the inbox already looks like a normal, trusted sender.

How long does it take?

Most teams warm a new inbox for two to four weeks before sending campaigns, then keep warmup running alongside them. See our guide on how long email warmup takes for a week-by-week plan.

inboxy warmup uses a private network of real inboxes to do this for you, on inboxy mailboxes or on Gmail, Microsoft 365 and SMTP inboxes you already own. See how inboxy warmup works.