Inkbox (inkbox.ai, YC S26) makes an argument worth taking seriously: an agent needs an identity, not an inbox, and identity spans channels. So an Inkbox agent gets an email address, a VoIP number with SMS and voice, iMessage, an agent-to-agent channel, a credential vault and a public tunnel — with memory that carries across all of them. Nothing in this category is doing that.
Bottom line: if you need the phone, buy the bundle. If you need email — which is what most agent workloads actually run on — you are paying a large multiple for channels you will not use. Ten agent identities cost $30/mo on Inkbox; fifteen inboxes cost $5/mo on Dead Simple Email. A hundred agent identities cost $200/mo on Inkbox; a hundred inboxes cost $29/mo on Dead Simple Email. And Dead Simple Email carries its own identity layer — an OIDC provider where the inbox is the login — free on every plan.
Pricing Comparison
Figures as read on 2026-09-16.
| Tier | Dead Simple Email | Inkbox |
|---|---|---|
| Free | 5 inboxes · 5,000 emails/mo | 3 agent identities · shared iMessage · 1 GiB per mailbox |
| Entry paid | $5/mo — 15 inboxes, 15,000 emails, 1 domain | $30/mo — 10 identities, 1 VoIP number, 10 domains |
| Mid | $29/mo — 100 inboxes, 100,000 emails | $200/mo — 100 identities, 10 VoIP numbers |
| Scale | $99/mo — 500 inboxes, 500,000 emails | Custom above 100 identities |
| Cost per agent at 100 | $0.29 | $2.00 |
| Metered extras | $0.40 per extra inbox, $0.20 per 1,000 emails | $0.03 per SMS, $0.03 per call minute, $20/mo per 10DLC campaign |
The $200 tier is the interesting one. It caps at 100 identities with 3 GiB per mailbox; Dead Simple Email's $99 plan carries 500 inboxes. If your fleet is large and email-shaped, the gap is close to an order of magnitude.
Feature Comparison
| Feature | Dead Simple Email | Inkbox |
|---|---|---|
| Email inbox per agent | Yes | Yes |
| Phone number, SMS, voice | No — email only | Yes — metered on top of the plan |
| iMessage | No | Yes |
| Agent-to-agent channel | Email, which every agent already speaks | Yes — proprietary channel |
| Credential vault | No | Yes |
| Public tunnel / URL | No | Yes |
| IMAP / SMTP | Yes | Yes |
| MCP server | Yes — in the official MCP registry | Yes |
| Agent identity / OIDC sign-in | Yes — Sign in with Dead Simple, free on every plan | Identity is the product, but not an OIDC provider |
| Verification-code / OTP extraction | Yes — dedicated endpoint | Not advertised |
| Prompt-injection scanning | Yes — scored on every inbound | Not advertised |
| Pay per request without an API key | Yes — x402 USDC and Stripe MPP | Agent self-signup |
| Published ceiling | 500 inboxes at $99 | 100 identities at $200, then custom |
When the Bundle Is Worth It
Honestly: when your agent has to talk to people who will not email it. Consumer-facing scheduling, delivery coordination, anything where the other party texts. SMS-based verification on services that refuse email OTPs. Voice. If those are on your roadmap this quarter, one vendor that carries all the channels under one identity is a real simplification, and Inkbox is the only one doing it.
What to price in: numbers are cheap in this market — roughly $3 per number, $0.02 per SMS and $0.13–$0.22 per voice minute from the specialist vendors — so a bundle is convenience, not savings. Inkbox meters SMS at $0.03 and minutes at $0.03, and a 10DLC campaign is $20/mo on top. Running Dead Simple Email for email and a telephony vendor for the phone is usually cheaper and always more replaceable.
Who Should Use Dead Simple Email
- Email-shaped workloads, which is most of them: support, recruiting, procurement, scheduling with businesses, verification, monitoring.
- Fleets above 100 agents, where Inkbox moves to custom pricing and Dead Simple Email is still $99 for 500.
- Teams that want agent identity as a standard, not a channel bundle — Sign in with Dead Simple is an OIDC provider where the agent's inbox is the login, free on every plan.
- Anyone evaluating without a budget line yet. Five inboxes free, no card.
Frequently Asked Questions
As of September 2026 Inkbox is free for 3 agent identities, $30/mo for 10 identities with one VoIP number, and $200/mo for 100 identities with ten numbers, with SMS at $0.03 and call minutes at $0.03 on top. Dead Simple Email is free for 5 inboxes, $5/mo for 15, $29/mo for 100 and $99/mo for 500. For an email-only workload at 100 agents that is $29 against $200.
No. Dead Simple Email is email infrastructure. Phone numbers for agents are a commodity in 2026 — roughly $3 per number with per-message and per-minute metering from specialist vendors — so we recommend pairing a telephony provider with Dead Simple Email rather than paying a bundle premium for a channel you may not use.
Dead Simple Email. It gives every agent a real inbox with IMAP and SMTP, an MCP server in the official registry, verification-code extraction, prompt-injection scanning, bulk provisioning, and an OIDC identity provider where the inbox is the login — at $5/mo for 15 inboxes against Inkbox's $30 for 10 identities.
Inkbox positions identity as its product, in the sense that one agent identity spans email, phone, iMessage and a vault. It is not an OIDC provider, so third-party applications cannot accept an Inkbox identity as a login. Dead Simple Email runs Sign in with Dead Simple, a standards-compliant OpenID Connect provider, free on every plan.
When your agent genuinely needs to be reachable by phone, SMS or iMessage as well as email, and you would rather buy that from one vendor than assemble it. Inkbox is the only product in this category bundling all of those under a single agent identity, and the bundle is worth real money if you need it.
Yes, and for large fleets it is usually cheaper. Run Dead Simple Email for the email channel at $29 per 100 inboxes, and buy numbers from a telephony vendor for the agents that actually need to text or call. You pay for the phone only where it is used.
All Inkbox figures on this page were read from its public pricing page on 2026-09-16 and are reproduced for comparison. Vendors change prices; check the source before making a decision, and tell us if anything here is out of date. Full cross-vendor tables: AI agent email API pricing comparison.