Why free-tier email APIs cap at 100/day, the wrong limit
A common free-tier pattern in this space is a small daily send cap, often around 100 emails a day. That number is designed to look generous ("3,000 a month!") while actually constraining you in the moment it matters most: a real traffic spike. Envello's free tier is 3,000 emails a month with no daily cap, and the difference is worth explaining, since it's not just a marketing detail.
Why a daily cap breaks at the wrong time
A daily limit assumes your sending is evenly distributed, which it usually isn't. A product launch, a marketing push, a batch of password resets after a security incident, real transactional email volume clusters around specific days, not a flat rate. A 100/day cap means your worst day, the one where sending actually matters most, is exactly when you hit the wall.
A concrete example of where this bites
Say you launch on Product Hunt and get 400 signups in a day, each triggering a welcome email and an email verification link. That's 800 emails on a day you specifically want every one of them to arrive fast. A 100/day cap means 700 of those either queue for the next several days or fail outright, right as new users are forming their first impression of your product. The free tier's whole purpose, letting you validate a real product with real users before paying, breaks exactly when it's being tested hardest.
Why a monthly cap without a daily sub-limit is the honest version
3,000 emails a month with no daily cap means you can send all 3,000 in one day if that's when you need them, or spread them out, without artificial throttling in either direction. It's the same total commitment from the provider's side (they're still capping total free usage), it just doesn't pretend a smooth daily rate is how real applications actually send email.
What happens when you actually hit 3,000 for the month
Sends beyond the monthly limit are rejected with a clear error rather than silently queued or throttled, so your application knows immediately rather than discovering a backlog later. At that point the honest options are upgrading to Pro (starting at 50,000 emails/month) or waiting for the next billing cycle if the volume was a one-off spike rather than a sustained pattern. Either way, you find out in the API response, not by noticing emails never arrived.
Why providers default to daily caps anyway
A daily cap is partly a spam-prevention mechanism: it limits how much damage a compromised free account can do before it's noticed and suppressed. That's a legitimate concern, but it's solvable with better abuse detection (rate-of-change monitoring, domain verification requirements, complaint-rate tracking) rather than by capping every legitimate free-tier user's worst day along with the rare bad actor's. A monthly cap combined with real abuse monitoring gets the same protection without the false-positive cost to normal usage patterns.