Mailbox Types · Guide
A new inbox has no history. To an inbox provider, a domain that has never sent anything and suddenly fires off fifty emails to strangers looks exactly like a spammer, because that is precisely what a spammer does. Warm-up is how you prove otherwise.
What warm-up actually is
You send a small, gradually increasing volume of email from a new inbox, and those emails get positive engagement: opened, replied to, marked as important, dragged out of spam. Over a couple of weeks, the provider builds a picture of an account that real people correspond with. That picture is your reputation, and it is what buys you inbox placement when you start real outreach.
How long, and how much
Two weeks minimum. Keep warm-up volume above your real sending volume, since warm-up mail goes to a friendly network and is low risk. In practice that means:
- Google: warm at around 20 a day across the two weeks, then send real campaigns at up to 15 a day per inbox.
- Azure: warm at around 6 a day across the two weeks, then send real campaigns at 2 to 3 a day per inbox.
Rushing this is the single most common reason new infrastructure fails in week one, and it is completely self inflicted.
Warm-up tools
Most sending platforms include a warm-up network where accounts email each other and auto engage. Instantly and Smartlead both bundle it, and EmailBison is particularly strong for warm-up. They work, with one caveat: obvious warm-up networks that generate mechanical, identical engagement are increasingly detectable. Prefer tools that vary content and timing, and do not rely on warm-up as your only source of engagement.
Keep it running
Warm-up is not a phase you graduate from. Leave it running at a low level permanently, alongside real campaigns. It maintains the engagement signal even when a campaign gets a rough response, and it cushions you against the inevitable bad week.
The mistakes that waste a warm-up
- Sending real campaigns during week one "just to test."
- Jumping to full volume the day warm-up ends instead of easing in.
- Warming an inbox whose domain is not authenticated yet, so you are building reputation on a foundation that fails.
- Warming, then sending to an unverified list, and undoing it all in one afternoon.
Pre-warmed inboxes skip the wait. They arrive with history already built. That is the trade: time versus money. If you are launching a campaign this week, buying warmed infrastructure is often cheaper than the two to three weeks of revenue you would lose waiting for your own to mature. Frostmailer delivers Azure and Google mailboxes pre-warmed and ready to send.
Want this done for you?
Our Build and Release service stands up your entire cold email infrastructure: domains, mailboxes, authentication, warm-up, and tracking, all authenticated and ready to send. You skip the weeks of setup and start with campaigns.