What to ask before buying another thousand inboxes

Inbox capacity has become a commodity pitch: pick a number, get a price. But capacity is the easiest thing in outbound to buy and the least likely thing to determine whether the program works. Before adding another thousand inboxes, the questions worth asking are about everything around the inboxes.

The questions that separate providers

• How many inboxes per domain? Higher density may reduce the purchase price, but it also concentrates more sending activity on each domain. Ask for the provider's normal density and enforced maximum.
• What happens when a domain degrades? Listen for a process that covers rest, repair, replacement, and spare capacity, not just a support ticket. If domain failure is entirely your problem to notice, you are buying capacity rather than an operating layer.
• What signals do you watch, and how do they affect intervention? Ask about bounce composition, placement trends, and per-domain health. Also ask which signals are visible to customers and which are used internally by the operator.
• How does volume ramp? Treat promises of unrestricted full volume on fresh domains carefully. A serious answer should explain preparation, staged ramps, and the signals used to slow down.
• Who owns the domains and what's the exit? Know whether you can take domains with you, and what winding down costs.

Cheap capacity is priced for the day you buy it. Infrastructure is priced for month six.

Why the cheap quote usually costs more

The purchase price does not show the whole operating cost. Higher density, limited monitoring, unclear remediation, and repeated replacement can add downtime and rebuilding costs later. A lower-density, actively operated setup costs more to maintain because it includes more domains, more visibility, and a defined intervention process.

Evaluate the operating model

Buy the operating model, not the inbox count. If the provider's answers are about price and quantity, you've learned what you needed to know.

Use Mailrun's provider evaluation framework.