Mailbox Types
Key takeaway: Keep per inbox volume low and provider specific: 2 to 3 a day on Azure, up to 15 a day on Google. Two to three inboxes per domain. Scale by adding inboxes and domains, never by pushing existing ones harder.
The numbers that keep infrastructure alive are conservative on purpose. Sending a lot from a few inboxes is what gets you filtered. Sending a little from many inboxes is what keeps you in the inbox.
Per inbox, per day
Azure: 2 to 3 emails per inbox per day.
Google: up to 15 emails per inbox per day.
These are the volumes we recommend on warmed Frostmailer inboxes. They are lower than the numbers you will see thrown around elsewhere, and that is the point: low per inbox volume is what makes each inbox look like a person rather than a machine.
Per domain: 2 to 3 inboxes
More inboxes on a single domain concentrates risk. If the domain gets flagged, everything on it dies at once. Keep it thin so failures stay contained.
Scaling math
Work backwards from your target. Because per inbox volume is low, you scale with more inboxes, which is exactly why Azure's low cost per inbox matters.
Daily sends | Google inboxes (15/day) | Azure inboxes (3/day) |
|---|---|---|
300 | 20 | 100 |
1,000 | 67 | 334 |
3,000 | 200 | 1,000 |
10,000 | 667 | 3,334 |
At 2 to 3 inboxes per domain, divide the inbox count by 3 for domains. Add 10 to 20 percent headroom so you are never running every inbox at its ceiling.
Warm-up comes first
During the two week warm-up the numbers are lower and volume goes to a friendly network, not to cold prospects. Do not send real campaigns from an inbox until it is through the ramp.
Other limits worth respecting
Randomize the intervals. Sending exactly one email every 90 seconds is a machine signature. Vary the gaps.
Respect business hours. Sending at 3am local time to your recipient looks automated. Schedule to their timezone.
Watch reply capacity. If you are generating more replies than you can answer within a day, you are sending too much. Unanswered replies are wasted pipeline and a bad recipient experience.
The temptation you must resist: when you need more volume, the obvious move is to send more per inbox. That is precisely the move that gets you filtered. Scale by adding inboxes and domains, never by pushing existing ones harder. Frostmailer sells warmed Azure and Google inboxes in exactly the ratio this math calls for.
Want this done for you?
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