Outbound email inboxes, built and operated for you.
Domains and inboxes provisioned in hours, sequencer-ready — then warmed, rotated, watched, and repaired for you as you scale.
24,000 inboxes in one managed deployment
One customer's live deployment — domains and inboxes in a rotating, resting pool, with volume spread instead of stacked.
The expensive part was never the inboxes. It's operating them.
Every launch brings deadlines, volume targets, and expectations. The drag shows up in the work nobody wants to own: domains, DNS, Microsoft inboxes, warmup, sequencer handoff, and the question of what to do when signals move.
Every inbox you buy comes with an operating model.
Every domain and inbox we provision moves through a full lifecycle — built, prepared, launched, rotated, watched, and repaired — so capacity stays healthy as you scale.
Mailrun operating layer — capacity with a bench, a watch path, and a repair path.
Build
Prepare
Launch
Rotate
Watch
Bench / Repair
Everything senders burn time on, already handled.
No implementation theater, no handoff chain, no waiting on basic setup. The infrastructure side becomes one repeatable operating system.
Choose infrastructure by the signals it gives you after launch.
Pricing and inbox count matter. But no provider can honestly promise you a deliverability percentage — copy and list quality are yours. What infrastructure does control is domain health, warmup maturity, bounce truth, and repair timing, and the real test is whether your provider shows you those signals before a campaign is already damaged.
The easiest mistake is buying enough inboxes and not enough operational visibility. Scale only works when you can see which domains are healthy, which need time, and which should be pulled out of production.
Size your sending plan.
Set your domain count and density. We'll show maximum inboxes, estimated monthly capacity, and the right way to buy.
Fresh infrastructure, self-serve up to 40 domains.
See Plans & CheckoutA recent customer deployment: 2,400 domains and 24,000 inboxes. Provisioning is automated and scales by adding domains, not pressure — so the number you need is the number we build.
Practical infrastructure notes for outbound operators.
Using AI in Cold Email: Research, Risks, and Human Review
AI can reduce the time required to research, draft, and review outbound email, but the available evidence does not support replacing factual verification and human editorial control.
Read Article →The economics of a $2.50 inbox
Google sells the seat for $8.40. Someone is retailing it for $2.50. The price gap deserves an explanation, especially when the replacement guarantee covers the mailbox but leaves the buyer holding the operational loss.
Read Article →2 MIN READInfrastructureInbox density: why up to 10 per domain beats 50
High density looks efficient until domain reputation starts carrying the bill for every sender on it. A look at the math behind keeping headroom on every domain.
Read Article →Built for operators running serious outbound.
Agencies, in-house SDR teams, and founders running their own outbound — on the same domains and inboxes, operated the same way.
“We got 50 replies in our first day, and have consistently added Mailrun inboxes to our arsenal.”
“Booked 27 meetings in our first 48 hours of sending. The email train has left the station!”
“I'm totally impressed by the Mailrun team. The inboxes are best in class, and their C-level is approachable for deep-dive support, even on the weekends!”
“Mailrun has the best mailboxes I've used. They're built for performance and scale without issues, whether you're running 10 or 1,000.”
“My experience with mailrun.ai has been really great so far. The support was amazing and I had the mailboxes on warm-up literally after 10 hours or so of purchasing.”
“Very impressed with the overall service. Super fast, strong deliverability and they go over and beyond supporting where needed.”
Straight answers, no scare tactics.
Fees, domains, density, deliverability, and how to ramp volume without burning reputation.
See all FAQs →How many inboxes can I run per domain?+
Up to 10, and that's a hard ceiling. We'd rather add domains than crowd more inboxes onto one reputation-bearing asset.
Why cap density at 10 per domain?+
The domain carries the reputation. The more sending you pile onto one domain, the more a single bad signal can drag everything on it down. Low density keeps headroom and protects the client.
How fast do I get access?+
Provisioning is automated. For standard fresh infrastructure, order to mailbox access is generally a couple of hours or less.
Can I bring my own domains, or can Mailrun buy them?+
Both. Bring your own domains, or have Mailrun manage them. Deployments that require us to buy more than 40 domains are mapped on a short planning call so cost and timing are confirmed up front.
What is pre-warmed infrastructure?+
Prepared inventory for agencies that need a faster client launch path. Pre-warmed domains start at $19 per domain per month and include 5 inboxes each, with a 10-domain minimum. Purchase directly while inventory is available. Larger or custom deployments may require a short planning call.
How is this different from cheap SMTP or Workspace mailboxes?+
Different model, built for a different operating assumption. Mailrun is Microsoft / Azure infrastructure with low domain density, horizontal scale, automated provisioning, and a clear operating lifecycle — built for agencies that care about durable client sending, not the lowest possible mailbox price.
Build the sending plan your next launch deserves.
Tell us your sending target, domain count, sequencer, and timing. We'll confirm capacity and map the cleanest path to live — self-serve or sales-assisted.
Mailbox access in hours. Sending volume ramps with discipline.