Two to three weeks, from a handful of messages a day to the mailbox's working cap of eight to ten cold emails. The clock starts when warm-up starts, not when the domain is registered, so buy domains early and let them age while the ramp runs. Warm-up does not stop at the end of week three either; it drops to a maintenance level and keeps running for as long as the mailbox sends.
Published by emailcampaign.ai, which warms mailboxes as part of its service. Ranking answers to this question disagree, quoting anything from fourteen days to six weeks; the ramp below is the one we run.
The ramp, week by week
Every number here is total outbound for that mailbox, warm-up included.
Days one to three: two to five a day, warm-up only, no campaign traffic at all. Anything landing in junk gets rescued, because the rescue is the signal that teaches the filter.
Week one: five to eight a day, still warm-up. A bounce spike here means the DNS or the mailbox is wrong, not the volume.
Week two: eight to twelve a day. The first campaign sends, two or three at most, with warm-up counted inside the same cap.
Week three: the full cap, split between warm-up maintenance and campaigns.
Steady state: eight to ten campaign sends a day per mailbox, indefinitely. Extra volume comes from more mailboxes, never from a higher number here.
Why the answers you find disagree
Some sources say fourteen days, some four to six weeks, some two to four. They are measuring different things. Fourteen days is the minimum before a mailbox can carry any campaign traffic at all. Four to six weeks is how long a full fleet takes to reach planned volume when you stagger the starts. Two to three weeks is how long one mailbox takes to reach its own working cap, which is what people usually mean when they ask.
The variable that matters more than the number is whether warm-up traffic is being counted inside the daily cap. Teams that finish a two-week warm-up, start campaigns at ten a day on top of a warm-up still running at eight, and then wonder why placement fell have not run a three-week warm-up. They have run a mailbox at eighteen a day in week three.
What warm-up cannot fix
Warm-up builds a sending history. It does not repair a domain with no authentication, a list full of dead addresses, or a complaint rate above 0.1 percent. If placement is poor after a full ramp, the cause is somewhere else, and rewarming will not find it.
Can you buy the wait down
Not honestly. Pre-warmed mailboxes carry someone else's sending history, usually on a domain the vendor owns and sometimes on a domain you cannot take with you if you leave. Reviewers regularly report pre-warmed domains arriving with reputation already damaged. If a campaign has to start on a date, buy the mailboxes three weeks before that date.
Questions, answered straight
- Does warm-up ever stop?
- No. After the ramp it drops to a maintenance level and keeps running for as long as the mailbox sends. A mailbox whose only traffic is cold outbound looks different from one having conversations.
- Do I need to warm up a domain as well as a mailbox?
- They warm together. Reputation attaches to both, and the mailbox is the thing sending, so the ramp on the mailbox is what builds the domain's history too.
- How long for a mailbox on a domain that is already sending?
- Shorter, often one week, because the domain already has history. The new mailbox still needs its own, so start it at the floor rather than at the fleet's cap.
- Does warm-up mail reach my inbox?
- It should not. On this platform warm-up traffic never reaches the master inbox, so the replies you see are from real people.
Published 19 September 2026. Updated 19 September 2026. Written by the team that runs the infrastructure; numbers come from the platform's own provisioning and sending, and from the providers' published documentation at the time of writing.