coss.com vs AgentMail
AgentMail is a fuller email client for agents. coss.com Inboxes gives agents threads and replies on the platform that also sends your email and SMS.
Both give each AI agent its own address, keep mail as threads, extract the reply from the quoted conversation and send a webhook per message. AgentMail adds drafts, labels, WebSockets, IMAP and SMTP, and a calendar. coss.com Inboxes builds on its email product: the same domains, deliverability, suppressions, logs and API key as your transactional email.
At a glance
AgentMail's side was checked on against its own pages. Prices are list prices.
| Feature | coss.com | AgentMail |
|---|---|---|
| Free | 3 inboxes and 3,000 received emails a month | 3 inboxes, 3,000 emails a month (100 a day) |
| Paid | Per inbox: $0.99 per 30 inbox-days for the first 3,100; $0.24 per 30 inbox-days from 3,101 to 31,000; $0.045 per 30 inbox-days beyond 31,000 | Developer $20 a month (10 inboxes); Startup $200 a month (150 inboxes) |
| Most inboxes | 1,000 on Pro, 10,000 on Scale | 150 on Startup; up to unlimited on Enterprise |
| Addresses | At coss.com's inbound domain (no DNS setup; receive-only in live environments) or your own receiving domains | At AgentMail's domain, or custom domains on paid plans |
| Real-time events | Webhooks (inbox.message.received); coss listen while you develop | Webhooks and WebSockets |
| Threads and reply text | Threads, each message's extracted_text without the quoted conversation | Threads, reply extraction |
| Drafts and labels | — | Both |
| IMAP and SMTP | — | Both |
| Multi-tenancy | Projects and environments, sandbox and live | Pods |
| SSO | Scale and Enterprise | Social sign-in on every plan; OIDC and SAML on Enterprise |
| Same account | Transactional and marketing email, SMS, Verify, Risk | Calendar |
Which to choose
Both are good at what they do. Here is where each one fits better.
Choose AgentMail when
Your agent needs a full mailbox
Drafts for human review and scheduled sends, labels to track state, allow and block lists, and a calendar with invitations. coss.com Inboxes has none of these.
You connect over IMAP or WebSockets
AgentMail speaks IMAP and SMTP for ordinary mail clients, and streams events over a WebSocket without a public URL.
Agents send from a shared domain on day one
AgentMail's free inboxes send and receive at its domain. coss.com's live inboxes at its inbound domain only receive: sending needs one of your own domains.
Choose coss.com when
Your email is already on coss.com
Inboxes reply from the domains you send from, with the same deliverability, suppressions, delivery events and logs as your transactional email.
Agents that also text and verify
The same API key sends SMS, one-time codes and Risk assessments, so an agent's tools come from one SDK.
Priced per inbox, by the day
An inbox costs only the days it exists, so short-lived agent inboxes don't pay for a month.
Sandbox environments
Sandbox inboxes send and receive without touching production mail or your bill.
Moving from AgentMail
- 1
Set up receiving
Start at the environment's inbound domain with no DNS, or add your own receiving domain for addresses you already use.
Read the guide - 2
Create the inboxes
AgentMail's inboxes become coss.inboxes.create({ username, client_id }); client_id makes a repeat create return the same inbox.
Read the guide - 3
Move the event handler
Subscribe a webhook endpoint to inbox.message.received, read the thread with coss.inboxes.threads.get() and reply with coss.inboxes.messages.reply().
Read the guide
Questions
- Can a coss.com inbox send email?
- Yes, from one of your own domains, and every inbox can send in sandbox environments. Live inboxes at coss.com's shared inbound domain only receive.
- Does coss.com support IMAP for agent inboxes?
- No. coss.com inboxes are read through the API, the SDK, the CLI and the MCP server, with a webhook for each message. AgentMail offers IMAP and SMTP.
- How are coss.com inboxes priced?
- Every plan includes a few inboxes; beyond them an inbox is billed for each day it exists, and received mail by the thousand. The current rates are on coss.com/pricing.
- Does coss.com strip quoted replies?
- Yes. Each message in a thread has extracted_text, its own words without the quoted conversation or the signature, which is what an agent should read.
Sources
AgentMail's facts were checked on ; their pages are the final word on their prices and features.
The coss.com side
Try coss.com next to AgentMail.
A development key costs nothing and delivers nothing, so you can compare with real code.
Add coss.com to this project: read https://coss.com/llms.txt, get a development key with `npx coss-cli init --agents`, and build and test with it.