Blog · Email Infrastructure
April 10, 2025 · 6 min read
Email warmup is the process of gradually building a sender reputation for a new domain or inbox before sending cold outreach at scale. It is not optional and it is not a formality. A domain with no sending history that suddenly starts sending fifty cold emails a day will see most of them land in spam. Warmup prevents that.
The principle is simple: mail servers judge new senders by how recipients engage with their emails. Warmup tools send emails from your new inbox to a network of other inboxes that are configured to open, mark as important, and occasionally reply. This builds positive engagement signals before real prospects see your domain.
The minimum warmup period for a brand new domain is three weeks. Four weeks is better. Some teams warm up for six weeks before sending anything to a real prospect. The patience required here is real, but the alternative — skipping warmup and watching a month of cold email land in spam — costs more.
Warmup timeline depends on the tool you use, the target daily send volume, and the age of the domain. A domain registered last week needs more warmup than a domain registered six months ago. If you are using Google Workspace, the warmup period for the Workspace account itself is also a factor — Google limits new accounts to lower send volumes in the early weeks.
Start at ten to twenty warmup emails per day. Increase by five to ten per day each week. After three to four weeks, you should have a healthy reputation and can begin campaign sends at twenty to thirty emails per inbox per day — conservative limits that protect the reputation you built during warmup.
Most warmup tools handle the ramp automatically. Set your target volume and they increase gradually. Monitor your deliverability score inside the tool — most show a score that reflects inbox placement rate. Do not start campaign sends until the score is consistently above 90.
Warmup does not stop when your campaign starts. Most teams keep warmup running in the background — ten to fifteen warmup emails per day alongside campaign sends. This maintains the positive engagement signal that protects inbox placement even as real cold emails are going out.
If your campaign volume drops significantly — a holiday week, a client pause, a technical issue — do not restart at full volume immediately. The reputation built during warmup decays if the inbox goes quiet. Ramp back up over a week before returning to previous send levels.