The Exact Tech Stack We Use to Send 10,000 Cold Emails a Day
Troy Aitken breaks down every tool in the stack powering 10,000 cold emails a day — from lead sourcing to deliverability monitoring.
Sending at volume isn't complicated. It's just a lot of moving parts that need to work together without breaking. Here's the exact stack we use to hit 10,000 emails a day, and why each piece is there.
Where the Leads Come From
We pull from Apollo, ZoomInfo, and Seamless to source contacts. Depending on the campaign, we'll also layer in list providers like ListKit when we want something more curated or pre-filtered. No single source is perfect, so mixing them keeps list quality from becoming a bottleneck.
The goal at this stage is simple: get enough verified, targeted contacts flowing into the system that volume is never the limiting factor. Targeting is its own discipline, but from a pure infrastructure standpoint, you need multiple data sources if you're serious about scale.
Domains: Buy Cheap, Buy Often
We buy domains from Squarespace and Porkbun. Both are consistently among the cheapest options, and at the volume we operate, that matters. You're not building a brand on these domains, you're rotating them through campaigns, and some will eventually get burned. Keeping acquisition costs low is just good math.
We also have automations on the back end to get new domains set up and sending-ready fast. The faster a domain moves from purchase to warmed inbox, the less dead time in the system.
Sending Accounts: Google and Microsoft
For mailboxes, we use Google Workspace and Microsoft 365. If you're just getting started, those two are all you need, don't overcomplicate it with SMTP providers until you have a real reason to. We do bake in SMTP on certain setups, but for most use cases, Google and Microsoft handle it cleanly.
The key is spreading volume across enough accounts that no single inbox is sending at a rate that triggers spam filters. At 10,000 emails a day, you're running a lot of accounts. That's the reality of cold email infrastructure.
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Managing It All: Smartlead and Instantly
Smartlead and Instantly are where everything comes together. Both platforms let you connect and manage large numbers of inboxes from one place, and their master inbox features are genuinely useful, you're not jumping between accounts to track replies. Everything surfaces in one view.
These tools also handle sending schedules, rotation across inboxes, and sequence management. At scale, trying to manage this manually isn't an option. Pick one, learn it properly, and let it do the operational heavy lifting.
Deliverability: EmailGuard
The last piece is EmailGuard, which we use to monitor and optimize deliverability. This is the part most people skip until something goes wrong, and by then you've already damaged sending reputation across a chunk of your infrastructure.
EmailGuard gives us visibility into how our emails are actually landing, whether they're hitting inbox or getting filtered, so we can catch problems early and adjust before they compound. I'll put out more detailed documentation on this, but the short version is: at this volume, you need a dedicated tool watching deliverability. It's not optional.
Key Takeaways
Lead sources: Apollo, ZoomInfo, Seamless, and supplemental providers like ListKit. Use multiple sources.
Domains: Buy from Squarespace or Porkbun to keep costs low. Automate the setup process.
Sending accounts: Google Workspace and Microsoft 365. Skip SMTP complexity until you actually need it.
Campaign management: Smartlead or Instantly. The master inbox feature alone is worth it at scale.
Deliverability monitoring: EmailGuard. Don't wait for a problem to start watching your inbox placement.
Frequently Asked Questions
What lead sources does this stack use? Apollo, ZoomInfo, and Seamless are the primary sources. ListKit and similar list providers get added depending on the campaign.
Why buy domains from Squarespace or Porkbun specifically? They're consistently the cheapest options. At scale, you're buying and rotating a lot of domains, so keeping the per-domain cost low adds up to real savings over time.
Do I need an SMTP provider to send at this volume? Not necessarily. Google Workspace and Microsoft 365 handle the majority of use cases. SMTP gets added for specific setups, but it's not a requirement if you're starting out.
What does EmailGuard actually do? It monitors deliverability, tracking whether emails are landing in inbox or getting filtered, so you can identify and fix issues before they damage your sending reputation across your whole infrastructure.
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