diff --git a/.eslintrc.json b/.eslintrc.json
index bbfe948..650f7eb 100644
--- a/.eslintrc.json
+++ b/.eslintrc.json
@@ -294,6 +294,7 @@
 		"wrap-regex":                    "warn",
 		"yield-star-spacing":           ["warn", "after"],
 
-		"@typescript-eslint/no-empty-function": "off"
+		"@typescript-eslint/no-empty-function": "off",
+		"@typescript-eslint/no-unused-vars": ["warn", {"destructuredArrayIgnorePattern": "^_"}]
     }
 }
diff --git a/src/smtp/SMTPServer.ts b/src/smtp/SMTPServer.ts
index 007579b..b554de4 100644
--- a/src/smtp/SMTPServer.ts
+++ b/src/smtp/SMTPServer.ts
@@ -1,10 +1,11 @@
+import sendStatus, { type StatusOptions } from "./status.js"
 import Logger from "../Logger.js"
 import SMTP from "./SMTP.js"
 import User from "../models/User.js"
 import getConfig from "../config.js"
 import net from "net"
-import sendStatus from "./status.js"
 import tls from "tls"
+import { verify } from "argon2"
 
 const logger = new Logger("SMTPServer", "GREEN")
 
@@ -39,6 +40,14 @@ export default class SMTPServer {
 			content: ""
 		}
 
+		const auth: {
+			state: "none" | "waiting" | "authenticated",
+			user:  string
+		} = {
+			state: "none",
+			user:  ""
+		}
+
 		sock.on("data", async (data: Buffer) => {
 			const msg = data.toString()
 
@@ -63,8 +72,7 @@ export default class SMTPServer {
 			logger.log(`Received data: ${msg}`)
 			if (msg.startsWith("EHLO")) {
 				sock.write(`250-${getConfig("host", "localhost")}\r\n`)
-
-				// We dont have any smtp extensions yet
+				sock.write(`250-AUTH PLAIN\r\n`)
 				status(250, { message: "HELP" }) // was: 250 HELP
 			} else if (msg.startsWith("MAIL FROM:")) {
 				// The spec says we should reset the state if the client sends MAIL FROM again
@@ -73,7 +81,20 @@ export default class SMTPServer {
 					to:      [],
 					content: ""
 				}
-				const email = msg.split(":")[1].split(">")[0].replace("<", "")
+
+				const email = msg.substring(msg.indexOf("<") + 1, msg.lastIndexOf(">"))
+
+				if (email.endsWith(`@${getConfig("host")}`) && auth.user != email) {
+					// RFC 4954 Section 6:
+					// 530 5.7.0  Authentication required
+					// This response SHOULD be returned by any command other than AUTH, EHLO, HELO,
+					// NOOP, RSET, or QUIT when server policy requires
+					// authentication in order to perform the requested action and
+					// authentication is not currently in force.
+					status(530, "5.7.0")
+
+					return
+				}
 
 				logger.log(`MAIL FROM: ${email}`)
 				info.from = email
@@ -138,6 +159,7 @@ export default class SMTPServer {
 				// but that can be a security risk + it is also done with RCPT TO anyway
 				status(502)
 			} else if (msg.startsWith("EXPN")) status(502)
+			else if (msg.startsWith("AUTH PLAIN") || auth.state == "waiting") await SMTPServer.authPlain(msg, auth, info, status)
 			 else status(502)
 		})
 		sock.on("close", () => {
@@ -145,4 +167,64 @@ export default class SMTPServer {
 		})
 	}
 
+	static async authPlain(
+		msg: string, auth: { state: "none" | "waiting" | "authenticated", user: string }, info: { from: string, to: string[], content: string },
+		status: (code: number, options?: StatusOptions | `${bigint}.${bigint}.${bigint}` | undefined) => void
+	) {
+		if (auth.state == "authenticated" || info.from != "" || info.to.length != 0 || info.content != "") {
+			// RFC 4954 Section 4:
+			// After a successful AUTH command completes, a server MUST reject any
+			// further AUTH commands with a 503 reply.
+			// RFC 4954 Section 4:
+			// The AUTH command is not permitted during a mail transaction.
+			// An AUTH command issued during a mail transaction MUST be rejected with a 503 reply.
+			status(503)
+		}
+
+		if (auth.state == "none") {
+			if (msg.split(" ").length == 3) {
+				await SMTPServer.authenticateUser(msg.split(" ")[2], auth, status)
+
+				return
+			}
+
+			status(334)
+			auth.state = "waiting"
+		} else if (auth.state == "waiting") await SMTPServer.authenticateUser(msg, auth, status)
+	}
+
+	static async authenticateUser(
+		msg: string, auth: { state: "none" | "waiting" | "authenticated", user: string },
+		status: (code: number, options?: StatusOptions | `${bigint}.${bigint}.${bigint}` | undefined) => void
+	) {
+		const [_, username, password] = Buffer.from(msg, "base64").toString().split("\0")
+
+		if (!username || !password) {
+			status(501, "5.5.2")
+			auth.state = "none"
+
+			return
+		}
+
+		const user = await User.findOne({ where: { username } })
+
+		if (!user) {
+			status(535)
+			auth.state = "none"
+
+			return
+		}
+
+		if (!(await verify(user.password, password))) {
+			status(535)
+			auth.state = "none"
+
+			return
+		}
+
+		auth.state = "authenticated"
+		auth.user = `${username}@${getConfig("host")}`
+		status(235, "2.7.0")
+	}
+
 }
diff --git a/src/smtp/status.ts b/src/smtp/status.ts
index 3004f48..e924a93 100644
--- a/src/smtp/status.ts
+++ b/src/smtp/status.ts
@@ -61,6 +61,7 @@ const STATUS_CODES: Record<number, StatusCode> = {
 	504: { code: 504, ok: false, message: "Command parameter is not implemented" },
 	521: { code: 521, ok: false, message: "Server does not accept mail" },
 	523: { code: 523, ok: false, message: "Encryption Needed" },
+	535: { code: 535, ok: false, message: "Authentication credentials invalid" },
 	550: { code: 550, ok: false, message: "Requested action not taken: mailbox unavailable" },
 	551: { code: 551, ok: false, message: "User not local; please try %" },
 	552: { code: 552, ok: false, message: "Requested mail action aborted: exceeded storage allocation" },
@@ -86,7 +87,7 @@ const ENHANCED_STATUS_CODES: Record<`${number} ${EnhancedCode}`, EnhancedStatusC
 	"554 5.3.4":  { code: 554, ok: false, message: "Message too big for system",               class: 5, subject: 7, detail: 8 }
 }
 
-type StatusOptions = {
+export type StatusOptions = {
 	message?: string,
 	enhancedCode?: EnhancedCode,
 	args?: string[]