The SMTP2GO alternative for AI agents MailKite launches as an SMTP2GO alternative for AI agents that need to both send and receive email, offering a unified inbox with parsed JSON and a receive-reply loop. Unlike SMTP2GO's send-only relay, MailKite enables agents to read verification codes and replies without a second provider. The SMTP2GO alternative for AI agents SMTP2GO is a clean, drop-in SMTP relay for sending, but it can't receive email at all, so an agent that has to read verification codes or replies needs a second provider bolted on. MailKite which we build gives the agent a real inbox as parsed JSON with a receive→reply loop, and sends too. For developers wiring an autonomous agent to email. An autonomous agent’s email life is a loop: it sends a signup, an email comes back with a verification code, it reads the code, it continues. SMTP2GO covers exactly one arrow of that loop. It’s a send-only SMTP relay and API. Its webhooks report what happened to mail you sent delivered , open , click , bounce , spam , and its own support docs tell you to use your mailbox provider’s IMAP/POP for anything incoming. So the moment your agent needs to read mail, SMTP2GO isn’t in the picture and you’re standing up a second provider to do the receiving. Here’s the whole MailKite side of that loop: receive, think, reply. It runs as pasted on Node 18+ npm install mailkite express , and it’s lifted straight from our agent-inbox pillar /blog/give-your-agent-an-inbox/ because the shape doesn’t change per provider. python import express from "express"; import { MailKite } from "mailkite"; const app = express ; const mk = new MailKite process.env.MAILKITE API KEY ; const SECRET = process.env.MAILKITE WEBHOOK SECRET; app.use "/hooks/agent", express.raw { type: "application/json" } ; app.post "/hooks/agent", async req, res = { // signature check, replay window, constant-time compare — one call if MailKite.verifyWebhook req.headers "x-mailkite-signature" , req.body, SECRET { return res.sendStatus 401 ; } res.sendStatus 200 ; // ack fast; run the agent out of band const event = JSON.parse req.body ; if event.type == "email.received" return; // Body is untrusted INPUT, never instructions see the security note below . const answer = await runAgent { task: event.text, from: event.from.address, trusted: event.auth.spf === "pass" && event.auth.dmarc === "pass", } ; await mk.send { from: event.to 0 .address, // reply from the address it was sent to to: event.from.address, subject: Re: ${event.subject} , inReplyTo: event.id, // threads the reply html: answer.html, } ; } ; app.listen 3000 ; That’s a complete inbound-capable agent: it hears, thinks, and answers, and the identical handler shape exists for Python, Ruby, Go, PHP, and Java see the receiving docs /docs/receiving and sending docs /docs/sending . The companion demo repo https://github.com/mailkite/demo-smtp2go-ai-agent has the runnable version. Open it in StackBlitz https://stackblitz.com/github/mailkite/demo-smtp2go-ai-agent?file=server.mjs , run npm start , and fire the sample event to watch a parsed email land. Where SMTP2GO wins for agents, honestly Don’t rip out SMTP2GO if all your agent does is send . For pure outbound it’s genuinely one of the least fussy relays around: The line is clean: if the agent only emits messages, SMTP2GO is a fine, minimal choice and MailKite doesn’t undercut it on relay simplicity. This post is about the other half of the loop. What SMTP2GO asks of an agent builder The instant your agent needs an inbox a signup emails back a code, a customer replies, a task arrives by email , SMTP2GO has no seam for it. You run a second provider for receiving, and you own the plumbing between them: python // Outbound is easy — SMTP2GO is a drop-in relay. import nodemailer from "nodemailer"; const relay = nodemailer.createTransport { host: "mail.smtp2go.com", port: 587, auth: { user: process.env.SMTP2GO USER, pass: process.env.SMTP2GO PASS }, } ; await relay.sendMail { from: "agent@myapp.ai", to, subject, html } ; // Inbound has no SMTP2GO path. You stand up a SECOND mailbox and poll it: import { ImapFlow } from "imapflow"; import { simpleParser } from "mailparser"; const imap = new ImapFlow { host: "imap.fastmail.com", port: 993, secure: true, auth: { user: process.env.IMAP USER, pass: process.env.IMAP PASS }, } ; await imap.connect ; const lock = await imap.getMailboxLock "INBOX" ; for await const msg of imap.fetch { seen: false }, { source: true } { const mail = await simpleParser msg.source ; // MIME parsing is yours // SPF / DKIM / DMARC? re-derive them yourself before you trust the sender. await runAgent { task: mail.text, from: mail.from?.text } ; await imap.messageFlagsAdd msg.uid, "\\Seen" , { uid: true } ; } lock.release ; Two vendors, a long-lived IMAP connection to babysit, MIME parsing, dedupe, and sender authentication you re-derive by hand. Every stage below is yours to build and keep running: None of this is exotic. IMAP polling has worked for decades. But it’s a personal mailbox with a person’s credentials wired into a bot, a MIME parser you maintain, and an auth check you re-derive, all of it standing between “an email came in” and “the agent does something.” The comparison, no adjective inflation | SMTP2GO | MailKite | | |---|---|---| | Outbound send | SMTP relay + Email API | SMTP submission + Send SDK/API | | Inbound receive | None send-only | Parsed JSON webhook | | Agent inbox codes, replies, tasks | Needs a 2nd provider IMAP mailbox | Built in | | MIME parsing | Yours, on the 2nd mailbox | Done at the edge | | SPF/DKIM/DMARC on inbound | Re-derive it yourself | In the auth block | | Threading / reply-from | Yours to track | Resolved threadId , inReplyTo | | Webhooks | Outbound events only delivered , open , bounce | email.received an actual incoming message | | Run the agent for you | No | Route with action: 'agent' | | Free tier | 1,000 emails/mo send | 3,000 messages/mo in + out | The through-line: SMTP2GO wins on being a clean, no-frills relay for messages leaving your system. MailKite wins the half SMTP2GO doesn’t have, which happens to be the half an autonomous agent lives or dies on: reading the mail that comes back. What actually hits your agent’s webhook Here’s the incoming email, already decoded. No IMAP poll, no MIME parser, and the auth block means you never re-derive SPF/DKIM/DMARC to decide whether to trust the sender: { "id": "msg 2Hk9…", "type": "email.received", "from": { "address": "ada@example.com" }, "to": { "address": "agent@myapp.ai" } , "subject": "Re: invoice 1042", "text": "Looks good — approved ", "html": "