Short answer. Warm-up is the gradual ramp of mail volume from a new domain or IP so providers build a positive reputation. Start with dozens of emails to your most engaged subscribers and roughly double the volume every couple of days over 4–6 weeks. Blasting large volume from a cold domain almost guarantees spam folders or blocks.
Why warm up
Providers (Gmail, Outlook, Yahoo) do not trust new senders. Reputation is built on history: volume, engagement, complaint and bounce rates. Warm-up gives the system time to accumulate positive signals.
A cold domain is like a stranger who immediately shouts. Warm-up is a small-step introduction where each good contact raises trust.
Day-by-day volume schedule
| Day | Volume | Who to send |
|---|---|---|
| 1–2 | 50 | Most active subscribers |
| 3–4 | 100 | Active |
| 5–7 | 250 | Active |
| 8–10 | 500 | Engaged in last 30 days |
| 11–14 | 1,000 | Engaged in last 60 days |
| 15–21 | 2,500 | Expanding the base |
| 22–30 | 5,000–10,000 | Core base |
Warm-up principles
- Start with the most engaged — opens and clicks give positive signals;
- ramp volume smoothly, no more than ×2 per step;
- keep bounce low — clean the list beforehand;
- watch spam complaints — threshold 0.1%;
- do not blast the cold/unengaged part of the base early.
What to monitor during warm-up
- Bounce rate — a rise signals a dirty list;
- Spam complaints — above 0.1% slows the warm-up;
- Your MX/SMTP availability — send failures break the rhythm;
- Blocklisting of your IP/domain.
A pre-warm-up check
# before starting, confirm authentication is in place
dig +short TXT example.com # SPF
dig +short TXT sel._domainkey.example.com # DKIM
dig +short TXT _dmarc.example.com # DMARCWhere enterno helps
You run the warm-up and the campaigns through your ESP — enterno does not send mail. But we cover preparation and control: /email-check confirms SPF/DKIM/DMARC before launch, and during warm-up /monitors watches mail-server availability (ports 25/465/587) and blocklists, alerting via Telegram/Slack/email/webhook on any break in the sending rhythm.
FAQ
How long does warm-up take?
Usually 4–6 weeks to target volume; longer for large bases.
Warm up the domain or the IP?
Both are linked. On a dedicated IP you warm the IP; on a shared pool you warm the subdomain and domain reputation.
What if bounce spikes?
Pause the volume ramp, clean the list, and step back one rung in the schedule.
Can warm-up be sped up?
There is no safe way: speeding up raises the risk of spam filtering and blocking.
Next: check authentication, separate streams in transactional email and set up server monitoring.