Resources/Glossary/Cold email and lead gen
Email warmup is slowly raising how much a new mailbox or domain sends, so inbox providers learn to trust it before you run outreach. A new mailbox that jumps straight to high volume looks like a spammer and often ends up in the spam folder.
In one line
Slowly raising how much a new mailbox sends so inbox providers learn to trust it before you run outreach.
Inbox providers have no history on a new domain or mailbox, so they watch early behavior closely. Warmup builds a positive record: steady, low volume sending, messages that get opened and replied to, and few bounces or complaints. Volume then rises in small steps over several weeks.
Many outreach platforms include automated warmup, which exchanges messages between a network of mailboxes and marks them as important. It can help, but real engagement from real people counts for more. Sending first to contacts likely to reply is a strong natural warmup.
Warmup is not a one time job. Many teams keep low level warmup running alongside campaigns and pause or slow sending when bounce or complaint rates rise. If a mailbox starts landing in spam, cut volume first and look for the cause before warming it back up.
Recruiting teams often add new mailboxes or domains to scale outreach. Skipping warmup can burn a domain within days, forcing you to start over and possibly hurting the reputation of related domains. A patient warmup plan protects the time and money you put into your sending setup.
A staffing firm buys two new outreach domains and sets up three mailboxes on each. It sets SPF, DKIM and DMARC, turns on warmup and starts with a handful of sends a day to warm contacts such as past candidates. Over about a month it raises volume gradually, and only then starts cold campaigns, keeping each mailbox at a modest daily limit.
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It varies with the domain, provider and how much you plan to send. Many teams allow several weeks before cold outreach and keep raising volume slowly after that.
If it has sent normal mail for a long time, it has some history. If it has been inactive or you plan a big jump in volume, ramp up gradually to avoid sudden changes.
It can help recovery, but first fix the cause: bad lists, missing authentication or too much volume. Then reduce sending and rebuild engagement slowly.
Written by recruiters at Work Insiders. Part of the recruiting and HR tech glossary. Updated October 2026.
