Per-event metered pricing: why monthly tiers force over-commit

Monthly email tiers were designed for marketing-blast SaaS where send volumes are predictable and roughly the same every month. Agent traffic is not that. A support agent might send 10 emails on a quiet day and 1,000 on an incident day. A 2FA-bridge agent fires only when a human signs in. A document-parser agent spikes when a customer uploads a batch. Monthly tiers force you to over-commit for the spike and waste capacity on the quiet days.

The over-commit math

The current incumbent pricing for a 1,000-emails-per-month workload:

• Resend: $20/month for 50,000 emails. You use 1,000. You ate $20. Effective cost per email: $0.020.
• Postmark: $50/month for 100,000 emails. You use 1,000. You ate $50. Effective cost: $0.050.
• SendGrid Essentials: $19.95/month for 50,000 emails. Same shape.

The opposite scenario is also bad. A 5,000-email-per-month workload on Resend Free (3,000 cap) has to upgrade to the $20 tier and instantly access 47,000 emails of unused capacity. The pricing structure does not match how agent products actually scale.

Per-event metered pricing — the alternative

Per-event metered pricing means every event — a send, a parsed inbound, an opt-in classification — posts a usage record to Stripe. At month-end, Stripe issues an invoice based on aggregated usage. No tier. No minimum. The metered plan is coming soon; Free, Pro, and Scale ship first.

The mechanism is Stripe Metered Billing, the same billing primitive that OpenAI, Twilio, AWS, and most modern usage-based SaaS run on. We did not invent the mechanic; we built it into the foundation rather than retrofit it.

What an event costs

The published rate card:

EVENT TYPE                          PRICE
─────────────────────────────────────────
send                                $0.001
inbound (structured reply event)    $0.002
classification (opt-in)            +$0.003
  (intent, entities, urgency)
suppression update                  free
identity check                      free
agent.list_threads call             free

Reads against your conversation history, suppression list updates, and identity checks are free. You only pay when an actual email moves — in or out. Every inbound event carries injection_score and sender_reputation at no extra cost; the +$0.003 classification add-on (intent, entities, urgency) is opt-in per agent.

The agent product reality

Run the math on actual agent shapes:

• 10/day support agent: 10 sends × 30 days = 300 sends. Plus 200 parsed inbounds (replies). 300 × $0.001 + 200 × $0.002 = $0.70/month.
• Inbound-heavy triage agent: 5,000 parsed inbounds in a busy month. 5,000 × $0.002 = $10/month— before any sends.
• 1,000/day operations agent: 1,000 sends × 30 = 30,000 sends. 30,000 × $0.001 = $30/month.
• 2FA-bridge agent (50 sends/month): 50 × $0.001 = $0.05/month. The agent that exists for one specific job pays one specific amount.

Same agent shape, different volumes, proportional cost. Compare to Resend at $20 flat regardless of whether you sent 1,000 or 30,000.

Why incumbents cannot match

Resend, Postmark, SendGrid, and Mailgun all built their economics around monthly tiers. The over-commit IS their gross margin — the difference between what customers pay and what those customers actually use. Switching to per-event pricing would cannibalize existing revenue at every renewal.

Amazon SES has true per-event pricing ($0.10 per 1,000 emails). But SES is raw infrastructure — no agent primitives, no structured reply events, no injection scanning, no per-agent reputation, no MCP server. You build all of that on top yourself.

Mails.ai puts agent-native primitives on top of a per-event pricing foundation. Both sides matter. The primitives without per-event pricing leaves customers over-committing for predictable volume on bursty workloads. Per-event pricing without primitives leaves them building their own classifier, parser, and reputation graph on top of SES.

Inspecting per-event costs in your dashboard

Live usage updates as your agent sends. The dashboard shows today, this month, and a projected month-total based on current rate:

TODAY                                $0.20
─────────────────────────────────────────
sends                    50  × $0.001   $0.05
parsed inbound           30  × $0.002   $0.06
classification (opt-in)  30  × $0.003   $0.09

THIS MONTH (so far)            842 events   $2.11
PROJECTED MONTH                              $2.48
LAST MONTH                    1,891 events  $4.73

Same data is exposed via the GET /v1/usageendpoint for programmatic consumption — useful if your agent needs to throttle itself based on remaining budget.

When to choose monthly vs metered

The right plan depends on volume predictability:

• Monthly Pro / Scaleif your agent has stable, predictable volume. At full included volume the monthly plans are far cheaper per event than metered — Pro’s 50,000 sends + 50,000 inbound would cost $150 metered versus $20 flat.
• Metered (coming soon) if your agent volume is bursty, seasonal, or unpredictable. Or if you are pre-launch and want to pay strictly for what your tests send.
• Freeif you are still prototyping — 3,000 events/month at $0.

You can swap plans month-to-month without contract penalties. The metered plan is the floor: even a 0-sends month costs $0.

Read the pricing page for the full plan table and the behavioral pool routing post for how deliverability pools actually work.