Email Warmup — Build Sender Reputation and Land in the Inbox

Email warmup is the process of gradually increasing a new or inactive mailbox's sending volume while generating authentic engagement — opens, replies, and inbox interactions — over two to three weeks. Mailbox providers such as Google and Microsoft score senders on that engagement history, so warmup builds the reputation that decides whether your email reaches the inbox, the promotions tab, or the spam folder.

Most mailboxes follow the same curve. Week 1 establishes a baseline sending pattern at low daily volume. Week 2 shows the first measurable lift in opens and replies. From week 3 onward inbox placement typically improves by 20-40%, and the full reputation benefit compounds over 4-8 weeks. Recovering a mailbox that has been landing in spam takes longer than warming a new one, because the negative history has to be outweighed first.

Yes. A new domain or mailbox has no sending history for providers to trust, so filters treat it as unproven and route its mail to spam or promotions by default. Sending campaign volume on day one is the fastest way to get a new domain flagged. Warmup gives providers a record of normal, engaged sending before real recipients ever see your outreach.

InboxWarm warms Gmail and Google Workspace, Outlook and Microsoft 365, Amazon SES, SendGrid, and Mailgun, plus any custom mailbox reachable over SMTP and IMAP. Gmail and Outlook connect with OAuth, everything else connects with standard SMTP and IMAP credentials, and mixed infrastructure warms under one account.

Start at roughly 2-5 emails a day in week 1, move to 10-15 by the end of week 2, and 25-30 by week 3, reaching 40-50 or more around day 30. InboxWarm applies that ramp automatically per mailbox, so you do not have to schedule it — the point is that daily volume never grows faster than the reputation supporting it.

It is safe when the sending looks human. InboxWarm uses real seed inboxes rather than bots, and keeps volume, timing, and reply behaviour inside normal human ranges, so providers see an active, healthy sender. The risk to a domain comes from the opposite pattern: sending high volume from a cold mailbox with no engagement history.

Yes, and it is one of the most common reasons people start. The process is identical — build fresh engagement signals from the current baseline — but recovery takes longer than warming a new mailbox because the existing negative history has to be outweighed before placement shifts. Pair warmup with fixing the cause, usually a volume spike, a bad list, or missing authentication.

No. Authentication and warmup solve different problems. SPF, DKIM, and DMARC prove you are allowed to send from your domain, and without them your mail can be rejected regardless of reputation. Warmup builds the engagement history that decides inbox placement once you pass authentication. You need both, and InboxWarm includes free tools to check each record.

InboxWarm starts at $15 per inbox per month for a single mailbox, and the per-inbox price drops with volume — $11 for 2-5 inboxes, $8 for 6-20, $6 for 21-50, and $5 for 51-100. Every plan starts with a 10-day free trial and no credit card is required.

No. Keep warmup running alongside your campaigns. Sender reputation reflects recent behaviour, so it decays when engaged sending stops, and warmup traffic cushions the periods when campaign replies are low. Most teams leave it on permanently for any mailbox they send outreach from.