Email Warmup
Gradually build your mailbox's sending reputation so your emails reliably reach the inbox instead of spam.
What is email warmup?
When a mailbox is brand new, email providers have no reputation data for it. Sending a large volume of emails from a cold mailbox triggers spam filters, causing your messages to land in junk folders -- or get blocked entirely.
Warmup fixes this by automatically exchanging real emails between your mailbox and Mailmark's network of platform accounts. These exchanges simulate genuine human email activity: messages are sent, opened, sometimes replied to, and rescued from spam folders. Over several weeks your domain accumulates positive engagement signals that inbox providers use to establish trust.
Warmup runs fully in the background -- you do not need to do anything once it is started. The Warming page in your dashboard shows live progress, health scores, and recent activity.
Requirements
Before you can start warmup, the following must be true for the mailbox's domain:
- SPF verified -- your SPF record authorises Mailmark's sending servers.
- DKIM verified -- your domain's DKIM keys are published and confirmed by AWS SES.
- DMARC verified -- a DMARC policy exists for your domain.
Speed plans
Choose a speed when you start warmup. Slower speeds are safer for domains that need to maintain a pristine reputation; faster speeds suit new domains where you need to reach sending volume sooner.
| Speed | Days 1-3 | Days 4-7 | Days 8-14 | Days 15-21 | Day 22+ |
|---|---|---|---|---|---|
| Slow | 2/day | 5/day | 10/day | 15/day | 20/day |
| Normal | 5/day | 10/day | 15/day | 20/day | 20/day |
| Fast | 10/day | 15/day | 20/day | 20/day | 20/day |
You can change speed at any time from the Warming dashboard. The daily limit adjusts immediately based on the new speed and the current warmup day.
Health score
Your warmup health score (0-100%) is a composite of three signals measured across recent warmup emails:
- Inbox placement (60% weight) -- what percentage of warmup emails landed in the inbox rather than spam.
- Open rate (20% weight) -- how many warmup emails were opened by the platform accounts.
- Reply rate (20% weight) -- how many warmup emails received a reply.
| Score | Status | What to do |
|---|---|---|
| 80-100% | Healthy | Continue warmup at current or faster speed. |
| 50-79% | Warning | Pause real sending, check DNS records, consider slowing warmup speed. |
| 0-49% | Critical | Pause warmup, audit domain reputation, verify DNS is correct. |
The score updates daily as new warmup emails are processed. A freshly started mailbox begins at 100% and moves up or down based on real engagement.
Best practices
- Do not send bulk campaigns during warmup. Keep real outbound sending minimal (under 20 emails/day) while warmup is active. Sudden volume spikes can counteract the reputation you are building.
- Keep DNS records intact. Removing or changing SPF, DKIM, or DMARC records mid-warmup will hurt your score. Only modify DNS records if instructed to do so during troubleshooting.
- Let it finish naturally. Pausing and resuming warmup frequently resets momentum. If you need to pause, keep it brief and resume as soon as possible.
- Monitor the health score weekly. A declining score early in warmup is a signal to investigate before it becomes a lasting reputation problem.
- One mailbox at a time per domain. Running multiple mailboxes through warmup simultaneously on the same domain is fine, but if your health score drops across all of them, pause all warmup sessions and investigate domain-level issues first.