Warm up a sending inbox before you need it

A new mailbox at full volume is a spam complaint with a countdown. This sets the ceiling, per inbox, and the conditions to raise it.

The play

1. Ramp by the age of the inbox, not the age of the campaign. Week one at a handful of sends a day; roughly double each week; reach full volume at about four weeks. Every seat runs its own clock — a new person joining a mature team starts at week one.
2. Get volume from more inboxes, never from one working harder. Two or three mailboxes on a domain, more domains when you need more volume. A single inbox pushed past its ceiling is the failure everyone repeats.
3. Send inside the recipient's working hours, on working days. Mail arriving at 3am local time reads as automation to a person and to a filter.
4. Keep the first touch plain. No links, no images, no tracking pixel, no attachment. Add them once a thread has a human in it.
5. Watch the three numbers that end a ramp: hard bounces (stop and clean the list well before 3%), spam complaints (any is a lot), and the share of sends that reach zero engagement over a week. A ramp is paused by evidence, not by feel.
6. Never warm up on the account you cannot lose. If cold volume must grow, put it on a separate sending domain and keep the primary one for real conversation.
7. Tell the user why the cap is low, in their words. A silent limit reads as a broken tool, and the person will raise it blindly to make the silence stop. Say the number, say the schedule, and if you offer a skip, spell out what it risks before they choose it.

What good looks like

• The tell: reputation is per sending identity, and it is earned by behaviour that looks like a person's — modest volume, replies coming back, activity inside a working day. Volume without replies is the pattern filters are built to catch, which is why the ramp exists at all and why a sequence that gets answers can climb faster than one that does not.
• The mediocre version warms up by mailing seed accounts in a warming network and calls the inbox ready on day three. The metric moves; the reputation does not. Nothing detectable happens until real volume starts landing in spam, and by then the domain is spent.
• You know the output is good when raising the cap changes nothing except the count — same bounce rate, same complaint rate, same reply rate. If replies fall as volume rises, the ceiling was already correct.

Rules

• MUST hold a per-inbox daily cap that increases with that inbox's own sending age.
• MUST pause the ramp on rising bounces or any complaint, and clean the list before resuming.
• MUST show the current cap and its reason wherever the user sees the send happening.
• NEVER run cold volume from the domain your business depends on.
• NEVER raise a cap silently, and never raise it without stating what a cold inbox at full volume risks.
• NEVER treat a warming-network score as evidence that a real list can be mailed.