Warm-up

Warm-up is the practice of slowly ramping up how many emails you send from a new domain or mailbox, so that inbox providers (Gmail, Outlook, and the rest) learn to trust you before you start sending in volume. Send too much, too fast, from a fresh address and the providers assume you're a spammer , your emails land in the junk folder and the whole campaign is dead on arrival.

The reason it works is simple: providers judge you on your track record. They watch your open rates, replies, spam complaints, and bounces. A sender who builds up gradually , a handful of emails a day, to people who actually engage , earns a good reputation. A sender who blasts thousands on day one has no track record, so they get filtered. Warm-up buys you that track record. A typical ramp runs two to eight weeks, starting small and with your most engaged recipients first, then widening out as the numbers stay healthy.

The practical rule: start low, watch your bounce and complaint rates like a hawk, send consistently (not in sporadic bursts), and only speed up once the signals stay clean.

Examples

• Cold outreach from a fresh domain. Say you're spinning up a new sending domain for a 50,000-prospect campaign in Instantly. Instead of pointing the full list at it on day one, you turn on automated warm-up, where the tool quietly sends and replies to a network of real mailboxes for a few weeks, then ramp your own sends from a few hundred a day to a few thousand. By the time you hit the cold list, the domain has a reputation and your mails actually reach inboxes.

• A multi-mailbox sequence. Say you're running cold outreach across ten mailboxes in Lemlist. You let each mailbox warm up for a couple of weeks first, capping daily sends low, then spread the campaign volume thinly across all ten rather than hammering one. The reputation builds in parallel and no single mailbox looks suspicious.

• A nurture campaign to existing customers. Say you're about to push a new automated nurture flow to 100,000 contacts in Brevo. You don't send to everyone at once , you start with your 10,000 most engaged contacts, watch the complaint and bounce rates for a few days, and only widen to the full list once those signals stay clean. The early engagement props up your reputation so the rest of the send lands.

A marketing platform launched a new automated nurture campaign to 100,000 existing customers. They implemented a one-week warm-up sending the first email to 10,000 highly engaged customers, monitoring response rates and complaints before expanding. Positive engagement signals allowed them to expand to 50,000 by day 4 and full list by day 7. The gradual warm-up resulted in zero spam complaints and strong engagement metrics. The same email sent without warm-up experienced slightly higher complaint rates suggesting some risk to sender reputation.

A sales team planned a cold outreach campaign targeting 50,000 prospects. Rather than sending to the full list immediately, they executed a four-week warm-up. Week one: 5,000 emails to warm leads (previous inquiries, inbound interest). Week two: 10,000 emails to warm segment with good engagement metrics. Week three: 25,000 emails to broader prospect list. Week four: full 50,000-person list. By maintaining this gradual approach, they achieved 35% inbox placement and 12% open rates - significantly higher than cold campaigns at the same company that skipped warm-up and achieved 8% inbox placement.

Execute email warm-up by first establishing a sending schedule and volume target. If your goal is to send 10,000 emails weekly, consider a four-week warm-up sending 2,500 in week one, 5,000 in week two, 7,500 in week three, and reaching 10,000 in week four. Start by sending to your most engaged recipients - existing customers, people who have previously engaged with you, or high-engagement segments. These recipients are more likely to open and engage, building positive sender signals.

Monitor key deliverability metrics throughout warm-up: bounce rate, spam complaint rate, and engagement metrics. If bounce or complaint rates are elevated, slow down the warm-up pace. Maintain consistent sending patterns rather than sending sporadically. Once you have completed warm-up and established positive sending patterns, you can expand volume more aggressively. Continue monitoring metrics post-warm-up to ensure your reputation remains strong.

Email warm-up directly impacts campaign effectiveness. If your emails are filtered to spam folders, the campaign is completely ineffective regardless of message quality. Warm-up ensures emails reach inboxes so recipients actually see your message. This is particularly critical for cold outreach campaigns where sender reputation is unknown to email providers.

For B2B growth teams relying on email for prospecting or customer nurturing, warm-up is essential for campaign success. A well-executed warm-up can mean the difference between emails reaching inboxes (50%+ open rates) and reaching spam folders (no engagement). The investment in proper warm-up directly impacts sales pipeline quality and lead generation effectiveness.

Warm-up also protects overall sender reputation. If you burn through your reputation with a poorly executed campaign, future legitimate emails from your domain are at risk. Investment in warm-up protects long-term email deliverability for your entire organisation.

A company expanded their outreach and added a new sending domain to increase capacity. Rather than transferring existing sending volume to the new domain immediately, they executed a two-week warm-up period. The new domain started with 1,000 emails daily to engaged recipients, expanding to 5,000 daily by week two. This deliberate approach established the new domain's reputation before reaching full sending capacity, preventing deliverability issues common when new domains begin sending high volumes immediately.