Domain reputation isn't declared, it's earned. Inbox providers track sending history per domain and IP over time, and there is no configuration setting that substitutes for that history. Warming is the process of building it deliberately, on a schedule, instead of hoping volume works itself out.
Why reputation has to be built, not declared
A domain with zero sending history looks identical, structurally, to a domain about to be used for abuse. The only signal that separates the two is behavior over time: consistent volume, low bounce rates, and real engagement in the form of opens and replies. Warming compresses the safest version of that behavior into a fixed schedule.
The six-week ramp
Week1
- Daily sends / mailbox
- 5-10
- Audience mix
- Internal or seed accounts that will open and reply
- What to watch
- Delivery confirms; no bounces expected
Week2
- Daily sends / mailbox
- 15-25
- Audience mix
- Small, highly engaged external segment
- What to watch
- Open rate should stay above baseline
Week3
- Daily sends / mailbox
- 30-50
- Audience mix
- Broader list, still filtered for quality
- What to watch
- Bounce rate creeping above 2%
Week4
- Daily sends / mailbox
- 60-100
- Audience mix
- Most of the intended list
- What to watch
- Spam complaint rate, reply rate trend
Week5
- Daily sends / mailbox
- 120-150
- Audience mix
- Full list
- What to watch
- Placement test results, blocklist status
Week6
- Daily sends / mailbox
- 150-200
- Audience mix
- Full list, steady state begins
- What to watch
- Week-over-week stability, not just one day
| Week | Daily sends / mailbox | Audience mix | What to watch |
|---|---|---|---|
| 1 | 5-10 | Internal or seed accounts that will open and reply | Delivery confirms; no bounces expected |
| 2 | 15-25 | Small, highly engaged external segment | Open rate should stay above baseline |
| 3 | 30-50 | Broader list, still filtered for quality | Bounce rate creeping above 2% |
| 4 | 60-100 | Most of the intended list | Spam complaint rate, reply rate trend |
| 5 | 120-150 | Full list | Placement test results, blocklist status |
| 6 | 150-200 | Full list, steady state begins | Week-over-week stability, not just one day |
Metrics to watch daily, not weekly
- Bounce rate: both the raw percentage and the split between soft and hard bounces.
- Spam complaint rate: even a handful of complaints on low volume is a meaningful signal in week one or two.
- Open rate relative to the list's historical baseline, where you have one.
- Reply rate: real engagement is the strongest positive signal a warming domain can generate.
- Blocklist status, checked against major lists at least once a day during the first three weeks.
When to pull back
Specific, not vibes-based: pull back if bounce rate exceeds roughly 3 to 5% on any single day, if spam complaints exceed roughly 0.1% of sends, or if a placement test shows mail landing outside the primary inbox on more than one major provider at once. Any one of these on its own warrants action; two together warrant stopping outbound from that domain until the cause is identified.
The pull-back sequence
Halve daily volume immediately, hold for 48 hours, re-run a placement test, and only resume the ramp from the week you were on (not from week one) once metrics recover.
Automating warmup with peer sends
Manually warming a domain by having colleagues email each other back and forth doesn't scale past a handful of domains. A private peer network (a pool of mailboxes across many domains that email, open, and reply to each other in patterns that mimic organic conversation) produces the same engagement signals at the volume a growing fleet actually needs, without exposing real prospects to a domain that hasn't proven itself yet.
What happens after week six
Reaching steady-state volume doesn't mean monitoring stops. It means the cadence relaxes from daily to weekly, as long as metrics stay stable for two consecutive weeks. A domain that goes quiet for more than roughly two weeks (a paused campaign, a mailbox on hold) should be treated as needing a partial re-warm, not resumed at full volume on day one back.