diff --git a/Apps/MagnumOpus/Services/AutoDiscovery.swift b/Apps/MagnumOpus/Services/AutoDiscovery.swift
new file mode 100644
index 0000000..730b583
--- /dev/null
+++ b/Apps/MagnumOpus/Services/AutoDiscovery.swift
@@ -0,0 +1,93 @@
+import Foundation
+
+struct DiscoveredServer: Sendable {
+	var hostname: String
+	var port: Int
+	var socketType: String
+}
+
+enum AutoDiscovery {
+	static func discoverIMAP(for email: String) async -> DiscoveredServer? {
+		guard let domain = email.split(separator: "@").last.map(String.init) else { return nil }
+
+		if let server = await queryISPDB(domain: domain) {
+			return server
+		}
+
+		if let server = await querySRV(domain: domain) {
+			return server
+		}
+
+		return nil
+	}
+
+	private static func queryISPDB(domain: String) async -> DiscoveredServer? {
+		let url = URL(string: "https://autoconfig.thunderbird.net/v1.1/\(domain)")!
+		guard let (data, response) = try? await URLSession.shared.data(from: url),
+			  let httpResponse = response as? HTTPURLResponse,
+			  httpResponse.statusCode == 200,
+			  let xml = String(data: data, encoding: .utf8)
+		else { return nil }
+
+		return parseISPDBXML(xml)
+	}
+
+	private static func parseISPDBXML(_ xml: String) -> DiscoveredServer? {
+		guard let imapRange = xml.range(of: "<incomingServer type=\"imap\">"),
+			  let endRange = xml.range(of: "</incomingServer>", range: imapRange.upperBound..<xml.endIndex)
+		else { return nil }
+
+		let section = String(xml[imapRange.upperBound..<endRange.lowerBound])
+
+		func extractTag(_ tag: String) -> String? {
+			guard let start = section.range(of: "<\(tag)>"),
+				  let end = section.range(of: "</\(tag)>", range: start.upperBound..<section.endIndex)
+			else { return nil }
+			return String(section[start.upperBound..<end.lowerBound])
+		}
+
+		guard let hostname = extractTag("hostname"),
+			  let portStr = extractTag("port"),
+			  let port = Int(portStr)
+		else { return nil }
+
+		let socketType = extractTag("socketType") ?? "SSL"
+		return DiscoveredServer(hostname: hostname, port: port, socketType: socketType)
+	}
+
+	private static func querySRV(domain: String) async -> DiscoveredServer? {
+		let candidates = [
+			"imap.\(domain)",
+			"mail.\(domain)",
+		]
+		for candidate in candidates {
+			if await testConnection(host: candidate, port: 993) {
+				return DiscoveredServer(hostname: candidate, port: 993, socketType: "SSL")
+			}
+		}
+		return nil
+	}
+
+	private static func testConnection(host: String, port: Int) async -> Bool {
+		do {
+			return try await withThrowingTaskGroup(of: Bool.self) { group in
+				group.addTask {
+					let task = URLSession.shared.streamTask(withHostName: host, port: port)
+					task.resume()
+					let (data, _) = try await task.readData(ofMinLength: 1, maxLength: 1024, timeout: 3)
+					task.cancel()
+					return data.map { !$0.isEmpty } ?? false
+				}
+				group.addTask {
+					try await Task.sleep(for: .seconds(3))
+					return false
+				}
+				let result = try await group.next() ?? false
+				group.cancelAll()
+				return result
+			}
+		} catch {
+			return false
+		}
+	}
+}
diff --git a/Apps/MagnumOpus/ViewModels/AccountSetupViewModel.swift b/Apps/MagnumOpus/ViewModels/AccountSetupViewModel.swift
index a2737c1..b1371d5 100644
--- a/Apps/MagnumOpus/ViewModels/AccountSetupViewModel.swift
+++ b/Apps/MagnumOpus/ViewModels/AccountSetupViewModel.swift
@@ -20,11 +20,19 @@ final class AccountSetupViewModel {
 	}
 
 	func autoDiscover() async {
+		guard !email.isEmpty else { return }
 		isAutoDiscovering = true
 		autoDiscoveryFailed = false
-		// Auto-discovery implementation in Task 16
-		isAutoDiscovering = false
-		isManualMode = true
+
+		if let server = await AutoDiscovery.discoverIMAP(for: email) {
+			imapHost = server.hostname
+			imapPort = String(server.port)
+			isAutoDiscovering = false
+		} else {
+			isAutoDiscovering = false
+			autoDiscoveryFailed = true
+			isManualMode = true
+		}
 	}
 
 	func buildConfig() -> (AccountConfig, Credentials)? {
diff --git a/Apps/MagnumOpus/Views/AccountSetupView.swift b/Apps/MagnumOpus/Views/AccountSetupView.swift
index 693455f..5131014 100644
--- a/Apps/MagnumOpus/Views/AccountSetupView.swift
+++ b/Apps/MagnumOpus/Views/AccountSetupView.swift
@@ -8,6 +8,11 @@ struct AccountSetupView: View {
 		Form {
 			Section("Account") {
 				TextField("Email", text: $viewModel.email)
+					.onChange(of: viewModel.email) { _, newValue in
+						if newValue.contains("@") && !viewModel.isManualMode {
+							Task { await viewModel.autoDiscover() }
+						}
+					}
 					#if os(iOS)
 					.textContentType(.emailAddress)
 					.keyboardType(.emailAddress)