Every few weeks I terminate an account for running warmup, and a day later I get an email that is genuinely baffled. They weren’t sending spam, they tell me. They were just warming up their domains. They paid for a nice tool that does it for them automatically. Everything was above board.
And that, right there, is the whole problem. Not that they were lying, because they usually aren’t. The problem is that warmup is the part of spam that happens before anybody would think to call it spam, and I am not willing to host it. Let me actually explain why, because the reasoning has always been more convincing to me than the rule.
If you’ve never touched cold email, warmup works like this. Before you start mailing a list of strangers who never asked to hear from you, you need the big providers to trust your sending domains. So a warmup service spins up a stack of mailboxes and has them email each other all day long, little fake back-and-forth conversations that mean nothing and were never meant to be read by a human. If you run a mail server of your own, you may have seen the wreckage of it in your logs without ever knowing what you were looking at: subjects like “Casual beach lunch” and “demo next week?” flying between addresses that have no earthly reason to be talking to each other. It is all theater, staged to manufacture a reputation out of thin air, so that when the real campaign finally goes out the domains look established and the filters wave them through. Warmup is the runway the real campaign takes off from. We don’t allow the warmup or the campaign, and that’s not buried in some terms document nobody reads. You click “I agree” to it on your way in the door.
Here’s the part the people running these tools never stop to think about, because the tool makes the whole thing feel clean and routine. When I pull the plug on a warmup account, it has nothing to do with etiquette or hurt feelings. I’m defending the inbox delivery of every other customer sharing those servers, and the way warmup threatens that is worth walking through slowly.
The big mailbox providers do not fight spam one message at a time. They look backward. When a campaign finally trips the wires, they can sit down and review everything that led up to it. Every domain that was involved. Every IP those domains ever touched. Every mail host that handled their traffic in the days and weeks before the campaign ever went out. Now picture them doing that not once but across hundreds of spam domains at the same time, hunting for what all those domains had in common on the way up. If those domains warmed up by relaying through us, guess what they all turn out to have in common. Us. We show up in the runup, over and over, right before the spam starts, attached to one bad domain after another.
At that point the damage has gone past anything as simple as a listed IP, which I can at least see and clear. I have handed Google a signal. “Mail from MXroute to a brand new domain” starts to look like a perfectly good early predictor that a spam campaign is about to happen. That is the thing that keeps me up at night: a quiet statistical association, learned by the largest filters on earth, that treats my own legitimate outbound mail as a warning sign. It would drag down delivery for everyone I host, and it would do it invisibly, in a way I couldn’t even point at until the complaints started rolling in from people who did nothing wrong at all.
And the tell, every single time, is the domains. A real business has a domain and guards it like it matters, because their reputation lives there and nowhere else. Warmup operations do the exact opposite. They burn through piles of throwaway domains on the cheapest TLDs they can find and rotate to fresh ones constantly, on purpose, by design. The disposable domain is there to absorb the blocklisting so the operator never has to feel it. They are deliberately arranging the whole thing so the cost lands somewhere other than on themselves.
Run that through a shared mail host and it is not hard to see where “somewhere other than themselves” actually points. It points at me, and through me, at every other customer on those IPs. They walk away with clean domains to burn next week. I’m left holding reputation damage that takes months to undo. And the person three accounts over who just wanted to run the email for their woodworking business gets worse delivery and never learns why. That trade, quietly shoving the cost onto strangers, is the entire reason warmup exists. It is also the entire reason I won’t be any part of it.
I know termination feels heavy-handed in the moment, especially when the tool made all of it feel so legitimate and routine. But the math isn’t close, and it was never going to be. One account running warmup can do damage that lands on thousands of people who never asked for any of it. I am not in a position to eat that on their behalf, and I wouldn’t even if I could, because the entire reason this company exists is so that the people paying me for real email get real delivery. That’s the job I asked you to pay me for, and you do.
So I catch these accounts early and I remove them. Not to punish anybody, though I understand that’s how it feels from the other side. I do it because protecting the reputation of this infrastructure and protecting you are the same sentence written twice. If I let warmup slide to keep one customer happy, I would be quietly selling out everyone else to do it, and I would rather lose the customer every time.
In the words of the great philosopher Sara Bareilles, “Who cares if you disagree.”
If you’re here to run your actual email, none of this will ever touch you, and you’ll probably never think about it again. That is the whole idea. Warmup isn’t welcome here, and that is precisely why your delivery is.