How inbox warmup works
What inbox warmup is, why it matters for deliverability, and how to start warmup for a new or cold inbox in CarcMail.
Start inbox warmup before you launch your first campaign. Even one to two weeks of warmup makes a significant difference to whether your emails land in the inbox or spam.
Overview
Inbox warmup is the process of gradually increasing the sending volume from a new or cold email inbox so that email providers (Gmail, Outlook, etc.) learn to trust it as a legitimate sender.
When a brand-new email address suddenly sends 200 emails in a day, spam filters notice. No established history, no positive signals — it looks suspicious. Warmup solves this by starting small (a handful of emails per day), getting positive engagement (opens, replies), and slowly scaling up over a few weeks.
CarcMail’s warmup feature handles this automatically. Once you start warmup on an inbox, CarcMail exchanges small, natural-looking emails with other inboxes in the CarcMail network. These emails get opened and replied to, building a reputation history with major email providers.
Why warmup matters
Email providers score senders based on their history. A low score means your emails go to spam even if the content is perfectly written. A high score means your emails consistently reach the inbox. Warmup is the fastest way to build that score safely.
Even an older inbox that hasn’t been used for outbound in a while can benefit from warmup before ramping up volume again.
Before you start
- The inbox is already connected to CarcMail (Gmail OAuth or SMTP)
- You are not sending high campaign volumes from this inbox yet
- You have at least 2 weeks before you plan to scale sending to 50+ emails per day
- The inbox has proper domain authentication set up (SPF, DKIM) — check with your IT or hosting provider
Step-by-step
Go to inbox settings
In the CarcMail sidebar, click Settings → Inboxes. Select the inbox you want to warm up by clicking its name.
Enable warmup
In the inbox detail panel, find the Warmup section. Toggle it to On. CarcMail will immediately start including this inbox in the warmup network.
Set your warmup goal (optional)
You can set a target daily volume — the maximum number of campaign emails you plan to eventually send per day from this inbox. CarcMail uses this to plan the warmup schedule. If you’re unsure, the default schedule is fine.
Monitor warmup progress
Return to the inbox panel at any time to see the warmup stage indicator. Stages progress roughly as follows:
- Days 1–7: 5–15 warmup emails per day
- Days 8–14: 15–40 warmup emails per day
- Days 15–21: 40–80 warmup emails per day
- Day 21+: Inbox is considered warm for moderate outbound volume
CarcMail will show a “Warmup in progress” badge and a recommended daily campaign limit at each stage.
Start campaigns alongside warmup
You don’t need to wait until warmup is complete to send campaigns. You can start low-volume campaigns (20–30 emails per day) during the warmup period. CarcMail will warn you if you try to send more than your current warmup stage supports.
How to confirm it worked
- The inbox shows a warmup progress indicator in the inbox settings panel
- Warmup emails appear in your sent folder (these are automatically filtered out of your reply and analytics views)
- After 2–4 weeks, the inbox health indicator turns green and the recommended daily limit increases
Do not disable warmup and immediately send high volumes. Warmup builds reputation gradually. Jumping from warmup to 200 emails per day overnight can still trigger spam filters.
Common issues
| Issue | What to check |
|---|---|
| Warmup emails going to spam | This can happen for the first few days. It will improve as the reputation builds. Keep warmup running. |
| Warmup seems stuck at the same stage | Warmup advances based on positive engagement. If your inbox provider is blocking warmup emails, contact support. |
| High campaign bounce rate during warmup | You may be sending too many real campaign emails too early. Lower campaign volume and let warmup continue. |
| Domain authentication warnings | SPF and DKIM records need to be set on your domain’s DNS. Ask your hosting provider to set these up. |
Frequently asked questions
A new inbox typically needs 2–4 weeks of warmup before it is ready for high-volume outbound. CarcMail starts conservatively and increases volume automatically.
Yes, but at lower volumes. CarcMail will warn you if your daily campaign volume exceeds what your warmup stage supports.
Warmup sends small, natural-looking emails between CarcMail network inboxes to build a positive engagement history for your sender.
Put it into practice
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