AI Agent Email API Pricing Comparison (September 2026)

Short answer: Dead Simple Email is the cheapest email API for AI agents at every fleet size with a published price, as of 16 September 2026. Giving 100 agents their own inbox costs $29/mo here, against $50 on Bavimail, $99 on Lumbox, LobsterMail or Mails.ai, $199 on Robotomail, $200 on AgentMail or Inkbox, $250 on Shipmail and roughly $700 on Google Workspace. At 500 agents it is $99/mo against roughly $900 on AgentMail and $589 on Nylas — and five of the vendors on this page do not publish a plan that reaches 500 inboxes at all.

Cheapest is only half the claim. The second half is the feature table: IMAP and SMTP on every inbox, webhooks with a delivery log and replay, SSE and WebSocket, an MCP server in the official registry with OAuth 2.1, prompt-injection scanning, verification-code extraction, bulk provisioning, an OIDC identity provider, and inbox creation paid per request with no account at all.

There are now more than twenty products selling email to AI agents, and almost none of them are directly comparable on price, because they meter different things: inboxes, messages, agents, operations, credits, domains, seats. This page normalises all of it into one question — what does my fleet cost per month? — and then shows the limits that turn a cheap plan into an expensive one.

If you want the per-vendor detail, every provider in the first table links to a full side-by-side page.

Every provider

Agent-native email APIs, all published prices

Products where an agent can own an inbox. Transactional send-only APIs are in a separate table, because they cannot do this job at any price.

Provider	Free tier	Entry paid plan	Top published plan	Cost per inbox at the top tier
Dead Simple Email	5 inboxes · 5,000 emails	$5 — 15 inboxes, 15,000 emails	$99 — 500 inboxes, 500,000 emails	$0.20
AgentMail	3 inboxes · 3,000 emails · 100/day	$20 — 10 inboxes, 10,000 emails	$200 — 150 inboxes, 15,000/day	$1.33 (+$2 per extra)
Robotomail	1 mailbox · 10 sends + 10 receives	$19 — 10 mailboxes, 15,000 sends	$199 — 200 mailboxes	$1.00
Lumbox	3 inboxes · 500 received + 100 sent	$9 — 10 inboxes	$99 — 250 inboxes, 50,000 sends	$0.40
LobsterMail	Unlimited inboxes · 1,000 emails	$9 — 10 inboxes, 5,000 emails	$99 — 300 inboxes, 100,000 emails	$0.33
Bavimail	6,000 emails · 3 inboxes per domain	$5 — 50,000 emails, 10 domains	$500 — 2,500,000 emails	Varies — capped per domain
Mails.ai	1 agent · 3,000 events	$20 — 5 agents, 50,000 sends	$99 — unlimited agents, 250,000 sends	n/a — agent caps by plan
Inkbox	3 agent identities	$30 — 10 identities + 1 phone number	$200 — 100 identities	$2.00
Shipmail	None — 14-day trial, card required	$4 — 2 mailboxes	$750 — 300 mailboxes at $2.50 each	$2.50
OpenMail	3 inboxes · 3,000 emails	€9 — 10 inboxes, 10,000 emails	Custom	€1.00 per extra inbox
Nylas Agent Accounts	3 accounts · 3,000 emails	$15 — 10 accounts, 10,000 emails	$49 — 50 accounts, 50,000 emails	$0.40 + $0.80 per 1,000 emails
Primitive	$0 with $5 of credits · 5 GB	$13 with $13 of credits	$299 with $299 of credits	n/a — metered, addresses on their domain
AGmail	Unlimited inboxes and emails on @agmail.ai	$15 — Pro, unlimited inboxes, 3 custom domains	$49 — Business, 10 custom domains, dedicated IP	n/a — priced on domains, not inboxes
DevInbox	1,500 operations · 1-hour retention	$12 — 10,000 operations, 24-hour retention	$99 — 100,000 operations, 15-day retention	n/a — metered per operation
MailSlurp	50 inboxes · 500 received	$19.99 — 100 inboxes, 1,000 received	$129.99 — unlimited inboxes, 5,000 received	n/a — capped on messages
InboxAPI	Free — @inboxapi.ai only, personal use	n/a	n/a	n/a
Hostinger Agentic Mail	None	From $0.39 per mailbox promotional, renews higher	Bundled with Business Email plans	Promotional pricing, per mailbox
Google Workspace	None	$7 per user	$7 per user, no volume tier	$7.00

Read from each vendor's own public pricing page on 16 September 2026. “Emails” means the monthly allowance a plan includes; where a vendor counts sends and receives separately, both are shown.

Cost at scale

What your fleet actually costs

Three fleet sizes, each with a realistic message volume. Every row is the cheapest plan at that vendor that genuinely fits the requirement, not the closest-sounding one.

10 agent inboxes, 5,000 emails a month

A small production fleet, or a team's first real deployment.

Provider	Plan that fits	Monthly cost	What you actually get
Dead Simple Email	Hobby	$5	15 inboxes, 15,000 emails, 1 custom domain
Bavimail	Developer	$5	50,000 emails, 10 inboxes on 1 domain
Lumbox	Starter	$9	10 inboxes, but only 2,000 sends
LobsterMail	Builder	$9	10 inboxes, 5,000 emails, 3 domains
OpenMail	Pro	€9 (~$10)	10 inboxes, 10,000 emails
DevInbox	Team	$12	10,000 operations, mail deleted after 24 hours
AGmail	Pro	$15	Unlimited inboxes, 3 custom domains, $5 each beyond
Nylas Agent Accounts	Essentials	$15	10 agent accounts, 10,000 emails
Robotomail	Developer	$19 ($9.50 for 3 months)	10 mailboxes, 15,000 sends, 500/day each
MailSlurp	Starter	$19.99	100 inboxes but only 1,000 received
AgentMail	Developer	$20	10 inboxes, 10,000 emails, 1,000/day
Shipmail	Team	$29	12 mailboxes, 120,000 sends, 25 GB each
Inkbox	Developer	$30	10 identities plus a phone number
Mails.ai	Scale	$99	Pro stops at 5 agents, so 10 needs Scale
Google Workspace	Business Starter	$70	10 human seats, suspension risk on bots

Cheapest: Dead Simple Email and Bavimail at $5. Dead Simple Email includes 15 inboxes rather than 10 and does not require a second domain to get there.

100 agent inboxes, 100,000 emails a month

One inbox per customer, or a mid-size swarm. This is where the category's price differences become obvious.

Provider	Plan that fits	Monthly cost	Notes
Dead Simple Email	Pro	$29	100 inboxes, 100,000 emails, 5 domains, nothing metered
Bavimail	Startup	$50	300,000 emails; 100 inboxes means 10+ domains
Lumbox	Scale	$99	250 inboxes but sends capped at 50,000
LobsterMail	Scale	$99	300 inboxes, 100,000 emails
Mails.ai	Scale	$99	Unlimited agents, 250,000 sends
DevInbox	Enterprise	$99	100,000 operations, mail deleted after 15 days
Nylas Agent Accounts	Pro + overage	~$109	$49 + 50 accounts at $0.40 + 50,000 emails at $0.80/1,000
MailSlurp	Pro	$49.99	Unlimited inboxes but only 5,000 emails — does not fit
Robotomail	Scale	$199	200 mailboxes; the $79 tier stops at 50
AgentMail	Startup	$200	150 inboxes; or $20 + 90 add-on inboxes at $2 = $200
Inkbox	Startup	$200	100 identities, 3 GiB each, phone metered separately
OpenMail	Pro + usage	~€189	€9 + 90 inboxes at €1 + 90,000 emails at €0.001
Shipmail	Scale	$250	100 mailboxes at $2.50 each
Google Workspace	Business Starter	$700	100 seats at $7

Dead Simple Email is the cheapest option that actually delivers 100 inboxes and 100,000 emails. The next agent-native plan that fits without a caveat is LobsterMail at $99, 3.4× the price.

500 agent inboxes, 500,000 emails a month

A platform giving every tenant an agent. Note how many vendors stop publishing prices here.

Provider	Plan that fits	Monthly cost	Notes
Dead Simple Email	Scale	$99	500 inboxes, 500,000 emails, 25 domains
Nylas Agent Accounts	Pro + overage	~$589	$49 + 450 accounts at $0.40 + 450,000 emails at $0.80/1,000
Shipmail	Scale	$750 for 300	Published ceiling is 300 mailboxes
AgentMail	Startup + add-ons	~$900	$200 + 350 extra inboxes at $2
Bavimail	Scale	$500	2,500,000 emails; 500 inboxes across many domains
Mails.ai	Scale + metered	$99 + overage	Unlimited agents, but 250,000 sends included
Robotomail	Custom	Not published above 200	Scale tops out at 200 mailboxes
Lumbox	Custom	Not published above 250	Scale tops out at 250 inboxes
LobsterMail	Custom	Not published above 300	Scale tops out at 300 inboxes
Inkbox	Custom	Not published above 100	Startup tops out at 100 identities
Google Workspace	Business Starter	$3,500	500 seats at $7

Five of the eleven vendors do not publish a price at this size at all. Dead Simple Email's $99 Scale plan is $0.198 per inbox per month, and inboxes beyond it are $0.40 each rather than a sales call.

Unit economics

Cost per inbox, per month

The number that matters if you are reselling agent inboxes or budgeting per tenant.

Provider	Top published plan	Inboxes included	Cost per inbox
Dead Simple Email	$99 Scale	500	$0.198
LobsterMail	$99 Scale	300	$0.330
Lumbox	$99 Scale	250	$0.396
Nylas Agent Accounts	$49 Pro + $0.40 each	50 included	$0.400 marginal, plus email metering
Robotomail	$199 Scale	200	$0.995
OpenMail	€9 Pro + €1 each	10 included	~$1.08 marginal
AgentMail	$200 Startup	150	$1.333 ($2.00 marginal)
Inkbox	$200 Startup	100	$2.000
Shipmail	$2.50 per mailbox	13–300	$2.500
Google Workspace	$7 per user	per seat	$7.000

Dead Simple Email's overage rate for inboxes beyond a plan is $0.40 each, which is still below every competitor's marginal rate except Nylas's, and Nylas meters email volume on top.

At $0.20 per inbox, an agent inbox costs less than the Stripe fee on the invoice that bills for it. That is the point: email should be a line item you stop thinking about, not one you architect around.

The other category

Transactional APIs are cheaper per message and cannot give an agent an inbox

Worth being precise about, because these products dominate the search results for “email API” and get recommended for agent work constantly.

Provider	Plan	Monthly cost	Inbound	Can an agent create its own inbox?
Amazon SES	À la carte at $0.10/1,000	~$10 + $15 Mail Manager inbound	Mail Manager or S3 + Lambda	No
Cloudflare Email Service	$5 Workers plan + $0.35/1,000	~$39	Email Routing to a Worker	No
Resend	Pro	$35	Limited	No
Mailtrap	Business	$85	Inbound addresses	No
Mailgun	Scale	$90	Routes	No
Postmark	Pro	~$134 ($16.50 + 90,000 at $1.30/1,000)	Pro and above	No
SendGrid	Essentials / Pro	From ~$20 at 50,000	Inbound Parse	No
Dead Simple Email	Pro	$29	Native — every inbox	Yes — one API call, or $1.00 with no account

SendGrid's pricing pages were redirecting in a loop on 16 September 2026; the figure shown is its published Essentials tier. Amazon SES and Cloudflare are cheaper per message than anything else here and neither can give an agent a mailbox it owns — you would be building the inbox, threading, storage, webhooks and retry logic yourself.

The distinction is not about volume pricing, it is about what exists. On a transactional API there is no object called an inbox. You cannot create one, an agent cannot own one, there is no thread history to read back, and inbound mail — where it exists at all — arrives as a parsed webhook against a domain, which you then have to store, thread, deduplicate and retry yourself. Teams that try it usually budget two to three weeks to build what amounts to a worse mailbox.

If your agent only ever sends, and never needs to read a reply, Amazon SES at $0.10 per thousand is genuinely the cheapest thing on this page and you should use it.

Cheap and complete

The feature side of the comparison

Low price usually means a thin product. Here is the same set of vendors on capability, with our own gaps marked honestly.

Capability	Dead Simple	AgentMail	Robotomail	Lumbox	LobsterMail	Nylas
Inbox creation via API	Yes	Yes	Yes	Yes	Yes	Yes
Bulk inbox create / delete	Yes	—	—	—	—	—
MCP server in the official registry	Yes	—	—	MCP tools	MCP server	—
MCP over OAuth 2.1	Yes	—	—	—	—	—
Webhooks on every plan	Yes	Yes	Yes	Paid only	Yes	Yes
Webhook delivery log + replay	Yes	—	—	—	—	—
SSE and WebSocket streaming	Both	WebSocket	SSE	Long-poll	—	—
IMAP and SMTP on every inbox	Yes	Yes	Yes	IMAP	—	Yes
Visual dashboard	Yes	—	Yes	—	—	Yes
Prompt-injection scanning	All plans	Beta, observe-only	—	—	Yes	—
Verification-code / OTP extraction	Yes	—	—	Yes	—	—
OIDC identity provider for agents	Free, all plans	AgentID	—	—	—	—
Pay per request, no API key	$1.00 inbox	$2.00 inbox	—	—	No key required	—
Stripe card payments over MPP	Yes	Tempo only	—	—	—	—
Domain purchase through the API	Yes	—	—	—	—	—
Threading, drafts, templates, contacts	Yes	Threading	Threading	Threading	—	Yes
Open and click tracking	Yes	—	—	—	—	—
First-party SDKs	Python, TS, Go, CLI	Python, TS, Go	REST, CLI	REST, MCP	TypeScript	Python, Node, Java, Kotlin
Framework integrations	19+	Several	REST	MCP	4	Several
SOC 2	—	Type II	—	—	—	Yes

Where a cell says —, the capability is not advertised on that vendor's public site as of 16 September 2026. Two honest gaps on our side: Dead Simple Email is not SOC 2 certified and does not sell dedicated IPs below enterprise.

Read the small print

What the headline price hides

Twelve things that change the real bill, and where each one applies.

What to check	Where it bites	Dead Simple Email
Daily send caps under the monthly allowance	AgentMail 100/day free and 1,000/day on $20; Robotomail 500/day per mailbox on $19; Mailtrap 150/day free; Resend 100/day free	No daily cap — the monthly allowance is the only limit
Add-ons that stack separately	AgentMail bills $2 per extra inbox, $2 per extra domain and $2 per extra 1,000 sends as three lines	$0.40 per extra inbox and $0.20 per 1,000 emails; domains are included by plan
Mail deleted after a retention window	DevInbox 1 hour to 15 days; MailSlurp storage caps from 200 MB	Messages retained within your plan's storage
Inbox limits counted per domain	Bavimail — 100 inboxes on the $5 plan means running and warming 10 domains	Inboxes counted per account, independent of domains
Send allowance far below receive allowance	Lumbox — 100,000 received against 50,000 sent on the $99 plan	One pooled allowance for sends and receives
Agent caps hiding inside “no per-inbox pricing”	Mails.ai — the $20 plan stops at 5 agents, so agent six costs $99	Inbox counts published on every plan
Usage credits rather than an allowance	Primitive — $13/mo buys $13 of credits metered across inbound, outbound, storage and function invocations	Flat tiers; a traffic spike does not change the bill
Every API call billed as an operation	DevInbox — one inbound that fires a webhook and is then fetched is three operations	API calls are free within your plan's rate limit
Introductory rates that step up	Robotomail — $9.50 for three months, then $19	Published price is the price
Card required to evaluate	Shipmail — 14-day trial with a card; Robotomail's free plan is 1 mailbox and 10 sends	Free forever, 5 inboxes, no card
Per-seat pricing applied to non-humans	Google Workspace at $7 per user; Zoho Desk from $7 to $40 per agent	Agents are not seats
Overage that silently stops instead of billing	Lumbox returns HTTP 402 at the cap	Paid plans run overage; free and trial plans stop rather than bill you

Methodology

Source. Every figure was read from the vendor's own public pricing page on 16 September 2026. Nothing here comes from a third-party listicle.
Plan selection. For each scenario we picked the cheapest plan at that vendor that actually satisfies both the inbox count and the message volume. Where no plan does, the row says so rather than quoting the closest one.
Arithmetic. Where a total combines a base plan with metered add-ons, the components are shown in the notes column so you can check the sum.
Currency. Euro prices are marked and converted approximately; we have not adjusted for exchange-rate movement.
Annual discounts. Monthly rates are used throughout except for DevInbox, whose published figures are annual, which is noted in its row.
Absent features. A dash means the capability is not advertised publicly, not that it is impossible. Vendors: if we have you wrong, tell us and we will correct it.

Sources

FAQ

Questions people actually ask

What is the cheapest email API for AI agents in 2026? +

Dead Simple Email, at every fleet size we could construct from published price lists on 16 September 2026. Its free plan carries 5 inboxes and 5,000 emails a month with no card; 15 inboxes cost $5/mo, 100 inboxes with 100,000 emails cost $29/mo, and 500 inboxes with 500,000 emails cost $99/mo. The nearest agent-native competitors at 100 inboxes are Bavimail at $50, LobsterMail, Lumbox and Mails.ai at $99, Robotomail at $199, and AgentMail and Inkbox at $200.

How much does it cost to give 100 AI agents their own email inbox? +

On published September 2026 pricing: $29/mo on Dead Simple Email, $50 on Bavimail, $99 on Lumbox, LobsterMail or Mails.ai, $109 on Nylas Agent Accounts, $199 on Robotomail, $200 on AgentMail or Inkbox, $250 on Shipmail, and about $700 on Google Workspace at $7 per user. Dead Simple Email's figure includes 100,000 emails a month and 5 custom domains.

What does AgentMail cost compared to Dead Simple Email? +

AgentMail is free for 3 inboxes and 3,000 emails, $20/mo for 10 inboxes, and $200/mo for 150 inboxes, with pay-as-you-go add-ons at $2 per extra inbox, $2 per extra domain and $2 per extra 1,000 sends. Dead Simple Email is free for 5 inboxes and 5,000 emails, $5/mo for 15 inboxes, $29/mo for 100 inboxes and $99/mo for 500. At 100 inboxes that is $29 against $200; at 500 inboxes it is $99 against roughly $900 once add-ons are stacked on the $200 plan.

What does Robotomail cost compared to Dead Simple Email? +

Robotomail is free for 1 mailbox with 10 sends and 10 receives, $19/mo for 10 mailboxes, $79/mo for 50 and $199/mo for 200, with an introductory rate of $9.50 for the first three months on the Developer plan. Dead Simple Email is free for 5 inboxes and 5,000 emails, then $5, $29 and $99 for 15, 100 and 500 inboxes. At Robotomail's top published tier a mailbox costs about $1.00 a month; on Dead Simple Email's top tier an inbox costs $0.20.

Is Dead Simple Email's free tier really free? +

Yes. Five inboxes, 5,000 emails a month, webhooks, IMAP and SMTP, the dashboard, the MCP server, verification-code extraction and prompt-injection scanning, with no credit card and no expiry date. Free and trial plans stop at their limits rather than running an overage charge, so a free account cannot generate a bill.

Which email APIs have hidden costs? +

The common ones in this category are daily send caps that sit under the monthly allowance, add-ons that stack (an extra inbox, an extra domain and extra sends billed separately), retention windows that delete mail after hours or days, per-domain inbox caps that force you to run and warm many domains, operations meters that count API calls as billable events, and introductory rates that double on renewal. Each one is listed with the vendor it applies to in the hidden-costs section of this page.

Are cheap agent email APIs missing features? +

Not necessarily, and this is the part worth checking rather than assuming. Dead Simple Email ships IMAP and SMTP on every inbox, HMAC-signed webhooks with a delivery log and replay, SSE and WebSocket streaming, an MCP server in the official registry with OAuth 2.1, prompt-injection scanning, verification-code extraction, bulk inbox operations, threading, drafts, templates, contacts, open and click tracking, Python, TypeScript and Go SDKs, a CLI, an OpenID Connect identity provider and pay-per-request access with no API key — at the lowest published price in the category.

Can transactional email APIs like Resend or Postmark work for AI agents? +

For sending only. Resend, Postmark, Mailgun, SendGrid, Mailtrap, Amazon SES and Cloudflare Email Service have no concept of an inbox an agent owns: you cannot create one through the API, and inbound mail arrives as a parsed webhook against a domain rather than as a mailbox with threads and history. They are cheaper per message at high volume and cannot do the job if your agent needs to hold a conversation.

What is the cheapest way to let an agent get its own inbox with no account? +

Dead Simple Email's pay-per-request route: an agent with a wallet calls POST /v1/inboxes with no credentials, receives HTTP 402 with the price, pays $1.00 inline in USDC over x402 (Base, Polygon or Solana) or with a Stripe card over MPP, and retries. AgentMail's equivalent x402 inbox creation is $2.00 as of September 2026, and its Stripe MPP support is limited to Tempo rather than cards.

How often is this comparison updated? +

Every figure on this page was read from each vendor's own public pricing page on 16 September 2026, and the page carries that date. Vendors change prices; if something here is stale, email hello@deadsimple.email and it will be corrected.

What an agent inbox actually costs, at 22 providers