How do they differ from ESPs like Mailchimp or SendGrid?
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If you've ever tried to run outbound prospecting through Mailchimp, you probably got a warning or had your account suspended. That's not a bug. It's by design. ESPs and cold email tools are built for completely different jobs, and mixing them up causes real problems.
Here's the core difference. ESPs send on your behalf through their own shared or dedicated infrastructure. You upload a list of people who already said yes to hearing from you, pick a template, and Mailchimp (or SendGrid, or Klaviyo) handles the delivery. They're optimized for volume, HTML design, A/B testing, and keeping a clean sender reputation across millions of sends per day.
Cold email tools work the other way around. Instead of sending through a shared infrastructure, they connect directly to your actual mailboxes, think Google Workspace or Outlook, and send through those. The emails look like they came from a real person sitting at a laptop, because technically they did. Lower volume, plain text, personalization tokens, and careful throttling to stay under the radar of sending limits. Tools like Lemlist, Instantly, and Smartlead are built for exactly this.
The compliance picture is also different. ESPs require opted-in subscribers by policy and often by law. Cold email tools are designed for outbound prospecting where no prior relationship exists. That doesn't mean cold outreach is a free-for-all (there are real legal frameworks depending on where you and your recipients are), but the tools themselves are built with that use case in mind.
To put it plainly: use an ESP for your newsletter, campaigns, and transactional emails. Use a cold email tool for prospecting sequences. Trying to use an ESP for cold outreach will get your account terminated. Trying to run campaigns to tens of thousands of subscribers through a cold tool will wreck your personal domain reputation fast.
Not sure which setup fits your situation? Take a look at how to choose the right tool for your use case, or drop us a note via the SOS hotline if you're trying to figure out the right stack for your business.
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