Direct Answer (Quick Summary)
Email warmup means building a new mailbox's sending reputation gradually before you use it for cold email. Set up SPF, DKIM and DMARC on a separate sending domain, then send a small number of real, engaging emails per day and increase slowly over two to four weeks. Most teams start around 5 to 10 emails a day, aim for 30 to 50 per mailbox per day once warm, and keep spam complaints well below 0.3%. Keep warmup running at a low level even after launch, and spread volume across several mailboxes instead of pushing one.
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What email warmup is and why it matters
Mailbox providers such as Gmail and Outlook judge every sender by its history. A brand-new mailbox that suddenly sends hundreds of emails looks exactly like a spammer, so its messages go to spam or are blocked. Warmup builds a history first: small daily volumes of real emails that are opened, replied to and rescued from spam, increasing step by step. Only once the mailbox looks like a normal, trusted sender do you start cold email campaigns.
Step 1: Use a separate sending domain
Buy one or more domains that are close to your brand (for example a variation with "get" or "try" in front) and use them only for outreach. Point the website of each sending domain to your main site so recipients who check it see a real business. Create two or three mailboxes per domain rather than dozens; a small number of real-looking mailboxes is safer than many.
Step 2: Authenticate the domain (SPF, DKIM, DMARC)
Authentication proves your emails really come from you. Set up all three records with your email provider's values before sending a single message.
Check before you warm
Contractor Leads checks SPF, DKIM, DMARC and MX for every connected mailbox and shows exactly which record is missing, so you can fix DNS before warmup starts rather than after deliverability drops.
| Record | What it does | What to check |
|---|---|---|
| SPF | Lists the servers allowed to send for your domain | One SPF record only, including your email provider |
| DKIM | Signs each email so providers can verify it was not altered | DKIM enabled in your provider and the DNS record published |
| DMARC | Tells providers what to do with mail that fails SPF/DKIM | Start with p=none and a reporting address, tighten later |
| MX | Lets the domain receive replies | Points to your email provider so replies arrive |
Step 3: Follow a gradual warmup schedule
Increase volume slowly and keep emails personal and two-way. A typical schedule for a new mailbox looks like this; slow down if inbox placement drops.
| Week | Warmup emails per day | Cold emails per day |
|---|---|---|
| Week 1 | 5-10 | 0 |
| Week 2 | 10-20 | 0 |
| Week 3 | 20-30 | 5-10 to your best-fit prospects |
| Week 4 | 20-30 | 20-30 |
| Week 5+ | 10-20 ongoing | 30-50 per mailbox |
Step 4: Protect your reputation while you send
Warmup only helps if your campaigns do not undo it. The biggest risks are bounces, spam complaints and sudden volume spikes.
- Verify every address before sending; aim for a bounce rate under 2%
- Keep spam complaints well below 0.3%, the threshold Google and Yahoo publish for bulk senders
- Include a clear way to opt out and honour it quickly
- Write short, specific, personal emails; avoid heavy images, many links and attachments in first touches
- Rotate across several mailboxes and keep each one within its daily limit
- Increase volume gradually, never in sudden jumps
Signs your warmup is working (or not)
Track inbox placement and engagement, not just how many emails went out.
| Signal | Healthy | Warning sign |
|---|---|---|
| Bounce rate | Under 2% | Above 3%: clean your list |
| Reply rate on cold email | Steady or rising | Sudden drop: check spam placement |
| Warmup emails landing in spam | Rare and decreasing | Rising: pause cold sends, keep warming |
| DNS checks | SPF, DKIM, DMARC all pass | Any failing record: fix before sending |
Common warmup mistakes
Most deliverability problems come from a few avoidable mistakes: sending cold email from the main company domain, skipping DKIM or DMARC, jumping from zero to hundreds of emails in a week, sending to unverified lists, and turning warmup off as soon as campaigns start. Fix these and you remove most of the risk. When your mailboxes are ready, pair them with well-written subject lines and a list of verified contractor emails so every send counts.
Frequently Asked Questions
How long does it take to warm up an email domain?
Plan on two to four weeks for a new domain and mailbox. Brand-new domains need the longest; older domains with a clean history can ramp faster. Watch inbox placement and replies rather than the calendar: if emails start landing in spam, slow down.
How many cold emails can I send per day from one mailbox?
Once a mailbox is fully warmed, 30 to 50 cold emails a day is a common safe range. To send more, add mailboxes and domains and rotate between them instead of increasing one mailbox's volume.
Do I need SPF, DKIM and DMARC for cold email?
Yes. Google and Yahoo require authenticated email from bulk senders, and unauthenticated mail is far more likely to be filtered. Set all three up before you start warming, and check them again after any DNS change.
Should I send cold email from my main domain?
No. Use a separate but similar domain, such as a variation of your brand name, for cold outreach. If its reputation is damaged, your main domain's everyday email is protected.
Should I stop warmup once I start sending campaigns?
No. Keep a low level of warmup running alongside campaigns. It keeps positive engagement flowing and helps you notice a reputation problem early.
Vaishali Kapoor
Founder, Contractor Leads
Vaishali leads product and growth at Contractor Leads, helping marketing agencies prospect, score, and close high-ticket home-service contractors.
