Choosing an email API plan: how to estimate your monthly volume

“How many emails will we send?” sounds like a question with an obvious answer, until you try to answer it. Sign-ups, password resets, receipts, alerts and digests all add up, and they grow with your user base in different ways.

This guide gives you a quick way to estimate your monthly volume, two worked examples, and how to match the number to an Inbixio plan with room to grow.

How Inbixio counts usage

Two facts make the estimate easier:

• One email = one recipient. Each API call sends to a single to_email, so a notification to 40 team members counts as 40 emails.
• Usage is counted per calendar month, and only emails that were sent successfully count toward your limit.

Inbixio’s plans:

See the pricing section for everything included in each plan.

Step 1: List every email your product sends

Open your codebase and search for every place that sends mail. Most products have three groups:

• Account emails: welcome, email verification, sign-in codes, password resets, security alerts.
• Activity emails: invitations, mentions, comments, approvals, task assignments, “your export is ready”.
• Billing emails: receipts, invoices, failed-payment notices, trial reminders.

Then add anything scheduled: daily or weekly digests, reports, reminders.

Step 2: Estimate each one per month

For each email, ask what triggers it and how often:

monthly emails = number of triggers per month × recipients per trigger

Use real numbers where you have them (sign-ups per month, active users, orders) and honest guesses where you don’t. It’s better to be roughly right than precisely wrong.

Example 1: an early-stage B2B SaaS

A project management tool with 2,000 active users and 400 new sign-ups a month:

That is well past Starter’s 25,000, but comfortably inside Growth’s 150,000, leaving room to more than double the user base.

Notice what dominates: notifications. If the number is too high, letting users choose instant or daily-digest notifications often halves it.

Example 2: a consumer app with sign-in codes

A mobile app with 8,000 monthly active users, all signing in with email codes about twice a month, plus a monthly receipt for 1,500 subscribers:

Starter covers it, with about 20% headroom. With growth expected, plan the move to Growth when you regularly pass 20,000.

Step 3: Add headroom for peaks

Monthly averages hide the spikes:

• Launches and press can triple sign-ups for a week.
• Imports and migrations can trigger thousands of invitations at once.
• Month-end billing concentrates receipts and failed-payment notices.

Add 30–50% to your estimate. If the result sits near a plan’s limit, choose the next plan up. When the limit is reached, further sends return 429 until the next month, and a missing password reset costs far more than the price difference. See handling email API errors and limits for what happens and how to monitor usage.

Step 4: Keep an eye on it

Your estimate is a starting point. Once you are live:

• The Usage Limit card on the API Keys page shows this month’s sent emails against your plan.
• The email volume chart on the dashboard shows sent and failed emails by month, so you can see the trend before you reach the limit.
• Review the number before big launches, imports or campaigns.

Quick guide

• Under ~20,000 a month with modest growth: Starter.
• 20,000 to ~120,000 a month, or growing quickly: Growth.
• Approaching 150,000, or needing 1M+, dedicated infrastructure or an SLA: talk to us about Enterprise.

Not sending yet? The five-minute quickstart gets your first email out, and you can change plans as your volume grows.