Why I run two separate email systems

This came up in someone else's thread here a few weeks ago, where I kept the details deliberately vague. Here is the full version, with names and costs.

RecoverStack sends emails from two fully separate systems, and this month I got an unplanned proof of it being a correct technical decision.

System 1 is for product email: waitlist confirmations, newsletters, and the payment-recovery emails that are integrated with the BL of the product. It runs on Resend, from the apex domain "recoverstack.dev". If these emails don't land, RecoverStack simply doesn't tick. This domain's reputation is the whole business.

System 2 is for cold outreach: Smartlead, sending from a Google Workspace mailbox on the subdomain "mail.recoverstack.dev", throttled to about 25 sends/day with warmup running. Cold email never touches the apex domain, not even once.

The reasoning is blast radius - cold email is the riskiest thing a company's email infrastructure does: a stranger who never asked to hear from you decides whether you're spam, and the sending domain absorbs every one of those judgments. Recovery emails are the exact opposite, they have to land or the product fails at its one job. Sharing a domain between those two is betting your core dependency & logic on the mood of strangers.

This month, the split got tested for real. Campaigns were running smoothly and starting to build traction, and then the suspension alert came in like thunder on a sunny day: Google had flagged the cold mailbox's logins as suspicious and suspended it. I spent three hours in Google support chats that went to the only path of deleting the mailbox entirely. This meant a new Workspace user, reconnecting Smartlead through OAuth, having the warmup history & spam-safe reputation score gone. That's a real cost, but it was contained entirely to the system that's allowed to die: the product side confirmed signups and fired drips the whole time like nothing happened.

This might surprise you, but the split cost me almost nothing extra. I needed Smartlead for the outreach automation anyway, the subdomain is a few (free) DNS records on top of the purchased domain, and finding the right setup is a quick search or one question to a coding agent. The only recurring tax is two dashboards and merging SPF entries by hand, because DNS setup wizards love to overwrite each other's records.

If you're a founder about to send your first cold campaign from the same domain your receipts and password resets use, please don't. This is one of the most damaging traps for a bootstrapped SaaS, and one of the easiest to avoid. One domain = one reputation = one point of failure. The safer setup is mostly free and a quick search away. Separate the inboxes and you'll hedge yourself from a lot of future trouble.

How is your email stack wired: one domain for everything, or split?