diff --git a/functions/infra/email_build_test.go b/functions/infra/email_build_test.go
new file mode 100644
index 00000000..c3dcae0e
--- /dev/null
+++ b/functions/infra/email_build_test.go
@@ -0,0 +1,125 @@
+package infra
+
+import (
+	"testing"
+)
+
+func TestEmailBuildHTML(t *testing.T) {
+	t.Run("construye mensaje html con campos basicos", func(t *testing.T) {
+		msg := EmailBuildHTML("alice@example.com", []string{"bob@example.com"}, "Hola", "<b>Hola</b>")
+		if msg.From != "alice@example.com" {
+			t.Errorf("From: got %q, want %q", msg.From, "alice@example.com")
+		}
+		if len(msg.To) != 1 || msg.To[0] != "bob@example.com" {
+			t.Errorf("To: got %v, want [bob@example.com]", msg.To)
+		}
+		if msg.Subject != "Hola" {
+			t.Errorf("Subject: got %q, want %q", msg.Subject, "Hola")
+		}
+		if msg.BodyHTML != "<b>Hola</b>" {
+			t.Errorf("BodyHTML: got %q, want %q", msg.BodyHTML, "<b>Hola</b>")
+		}
+	})
+
+	t.Run("copia el slice to para evitar aliasing", func(t *testing.T) {
+		to := []string{"a@example.com", "b@example.com"}
+		msg := EmailBuildHTML("x@x.com", to, "s", "h")
+		to[0] = "mutated@example.com"
+		if msg.To[0] == "mutated@example.com" {
+			t.Error("To slice was aliased — mutation affected the message")
+		}
+	})
+
+	t.Run("campos no usados quedan vacios", func(t *testing.T) {
+		msg := EmailBuildHTML("f@example.com", []string{"t@example.com"}, "s", "h")
+		if msg.BodyText != "" {
+			t.Errorf("BodyText should be empty, got %q", msg.BodyText)
+		}
+		if len(msg.CC) != 0 {
+			t.Errorf("CC should be empty, got %v", msg.CC)
+		}
+		if len(msg.BCC) != 0 {
+			t.Errorf("BCC should be empty, got %v", msg.BCC)
+		}
+		if len(msg.Attachments) != 0 {
+			t.Errorf("Attachments should be empty, got %v", msg.Attachments)
+		}
+	})
+}
+
+func TestEmailBuildText(t *testing.T) {
+	t.Run("construye mensaje text con campos basicos", func(t *testing.T) {
+		msg := EmailBuildText("alice@example.com", []string{"bob@example.com"}, "Alerta", "Servidor caido")
+		if msg.BodyText != "Servidor caido" {
+			t.Errorf("BodyText: got %q, want %q", msg.BodyText, "Servidor caido")
+		}
+		if msg.From != "alice@example.com" {
+			t.Errorf("From: got %q, want %q", msg.From, "alice@example.com")
+		}
+		if msg.Subject != "Alerta" {
+			t.Errorf("Subject: got %q, want %q", msg.Subject, "Alerta")
+		}
+	})
+
+	t.Run("body html queda vacio", func(t *testing.T) {
+		msg := EmailBuildText("f@x.com", []string{"t@x.com"}, "s", "body")
+		if msg.BodyHTML != "" {
+			t.Errorf("BodyHTML should be empty, got %q", msg.BodyHTML)
+		}
+	})
+}
+
+func TestEmailWithAttachment(t *testing.T) {
+	t.Run("agrega adjunto sin mutar el original", func(t *testing.T) {
+		orig := EmailBuildHTML("a@example.com", []string{"b@example.com"}, "s", "h")
+		att := EmailAttachment{Filename: "f.pdf", ContentType: "application/pdf", Data: []byte("data")}
+		msg2 := EmailWithAttachment(orig, att)
+
+		if len(orig.Attachments) != 0 {
+			t.Errorf("original was mutated: got %d attachments, want 0", len(orig.Attachments))
+		}
+		if len(msg2.Attachments) != 1 {
+			t.Errorf("got %d attachments, want 1", len(msg2.Attachments))
+		}
+		if msg2.Attachments[0].Filename != "f.pdf" {
+			t.Errorf("Filename: got %q, want %q", msg2.Attachments[0].Filename, "f.pdf")
+		}
+	})
+
+	t.Run("multiples adjuntos se acumulan", func(t *testing.T) {
+		msg := EmailBuildHTML("a@x.com", []string{"b@x.com"}, "s", "h")
+		msg = EmailWithAttachment(msg, EmailAttachment{Filename: "a1.txt", ContentType: "text/plain", Data: []byte("1")})
+		msg = EmailWithAttachment(msg, EmailAttachment{Filename: "a2.txt", ContentType: "text/plain", Data: []byte("2")})
+		if len(msg.Attachments) != 2 {
+			t.Errorf("got %d attachments, want 2", len(msg.Attachments))
+		}
+	})
+
+	t.Run("copia todos los campos del mensaje", func(t *testing.T) {
+		orig := EmailMessage{
+			From:     "a@x.com",
+			To:       []string{"b@x.com"},
+			CC:       []string{"c@x.com"},
+			BCC:      []string{"d@x.com"},
+			Subject:  "Test",
+			BodyHTML: "<p>Hi</p>",
+			BodyText: "Hi",
+			Headers:  map[string]string{"X-Test": "value"},
+		}
+		att := EmailAttachment{Filename: "f.png", ContentType: "image/png", Data: []byte("img")}
+		msg2 := EmailWithAttachment(orig, att)
+
+		if msg2.From != orig.From {
+			t.Errorf("From mismatch: %q vs %q", msg2.From, orig.From)
+		}
+		if msg2.Subject != orig.Subject {
+			t.Errorf("Subject mismatch: %q vs %q", msg2.Subject, orig.Subject)
+		}
+		if len(msg2.CC) != 1 || msg2.CC[0] != "c@x.com" {
+			t.Errorf("CC not copied: %v", msg2.CC)
+		}
+		if msg2.Headers["X-Test"] != "value" {
+			t.Errorf("Headers not copied: %v", msg2.Headers)
+		}
+	})
+}
diff --git a/functions/infra/email_template_render_test.go b/functions/infra/email_template_render_test.go
new file mode 100644
index 00000000..598badad
--- /dev/null
+++ b/functions/infra/email_template_render_test.go
@@ -0,0 +1,46 @@
+package infra
+
+import (
+	"strings"
+	"testing"
+)
+
+func TestEmailTemplateRender(t *testing.T) {
+	t.Run("renderiza template simple con datos", func(t *testing.T) {
+		got, err := EmailTemplateRender("Hola {{.Name}}", map[string]any{"Name": "Alice"})
+		if err != nil {
+			t.Fatalf("unexpected error: %v", err)
+		}
+		if got != "Hola Alice" {
+			t.Errorf("got %q, want %q", got, "Hola Alice")
+		}
+	})
+
+	t.Run("sustituye multiples variables", func(t *testing.T) {
+		tmpl := "Pedido {{.OrderID}} para {{.Customer}} listo."
+		got, err := EmailTemplateRender(tmpl, map[string]any{"OrderID": "ORD-42", "Customer": "Bob"})
+		if err != nil {
+			t.Fatalf("unexpected error: %v", err)
+		}
+		if !strings.Contains(got, "ORD-42") || !strings.Contains(got, "Bob") {
+			t.Errorf("got %q, expected OrderID and Customer", got)
+		}
+	})
+
+	t.Run("error en template invalido", func(t *testing.T) {
+		_, err := EmailTemplateRender("{{.Unclosed", nil)
+		if err == nil {
+			t.Error("expected error for invalid template, got nil")
+		}
+	})
+
+	t.Run("template vacio retorna string vacio", func(t *testing.T) {
+		got, err := EmailTemplateRender("", nil)
+		if err != nil {
+			t.Fatalf("unexpected error: %v", err)
+		}
+		if got != "" {
+			t.Errorf("got %q, want empty string", got)
+		}
+	})
+}
diff --git a/functions/infra/smtp_connect_test.go b/functions/infra/smtp_connect_test.go
new file mode 100644
index 00000000..dfdccf78
--- /dev/null
+++ b/functions/infra/smtp_connect_test.go
@@ -0,0 +1,120 @@
+package infra
+
+import (
+	"bufio"
+	"fmt"
+	"net"
+	"strings"
+	"testing"
+)
+
+// mockSMTPServer starts a minimal SMTP server on a random port that greets
+// and accepts any commands. Returns the listener address and a function to stop it.
+func mockSMTPServer(t *testing.T) (addr string, stop func()) {
+	t.Helper()
+	ln, err := net.Listen("tcp", "127.0.0.1:0")
+	if err != nil {
+		t.Fatalf("mock smtp listen: %v", err)
+	}
+	go func() {
+		for {
+			conn, err := ln.Accept()
+			if err != nil {
+				return
+			}
+			go handleMockSMTP(conn)
+		}
+	}()
+	return ln.Addr().String(), func() { ln.Close() }
+}
+
+// handleMockSMTP is a minimal SMTP session handler (no TLS, no auth required).
+func handleMockSMTP(conn net.Conn) {
+	defer conn.Close()
+	w := bufio.NewWriter(conn)
+	r := bufio.NewReader(conn)
+	fmt.Fprintf(w, "220 mock SMTP ready\r\n")
+	w.Flush()
+	for {
+		line, err := r.ReadString('\n')
+		if err != nil {
+			return
+		}
+		line = strings.TrimSpace(line)
+		upper := strings.ToUpper(line)
+		switch {
+		case strings.HasPrefix(upper, "EHLO"), strings.HasPrefix(upper, "HELO"):
+			fmt.Fprintf(w, "250 mock\r\n")
+		case strings.HasPrefix(upper, "MAIL FROM"):
+			fmt.Fprintf(w, "250 OK\r\n")
+		case strings.HasPrefix(upper, "RCPT TO"):
+			fmt.Fprintf(w, "250 OK\r\n")
+		case strings.HasPrefix(upper, "DATA"):
+			fmt.Fprintf(w, "354 End with .\r\n")
+			w.Flush()
+			// read until ".\r\n"
+			for {
+				dl, derr := r.ReadString('\n')
+				if derr != nil {
+					return
+				}
+				if strings.TrimSpace(dl) == "." {
+					break
+				}
+			}
+			fmt.Fprintf(w, "250 OK\r\n")
+		case strings.HasPrefix(upper, "QUIT"):
+			fmt.Fprintf(w, "221 Bye\r\n")
+			w.Flush()
+			return
+		default:
+			fmt.Fprintf(w, "502 Command not recognized\r\n")
+		}
+		w.Flush()
+	}
+}
+
+func TestSMTPConnect(t *testing.T) {
+	t.Run("conecta sin cifrado a servidor mock", func(t *testing.T) {
+		addr, stop := mockSMTPServer(t)
+		defer stop()
+
+		host, portStr, _ := net.SplitHostPort(addr)
+		port := 0
+		fmt.Sscanf(portStr, "%d", &port)
+
+		cfg := SMTPConfig{
+			Host:    host,
+			Port:    port,
+			TLSMode: "", // no encryption
+		}
+		client, err := SMTPConnect(cfg)
+		if err != nil {
+			t.Fatalf("SMTPConnect: %v", err)
+		}
+		client.Quit()
+	})
+
+	t.Run("error si el servidor no existe", func(t *testing.T) {
+		// Use a port that is listening but immediately closes (RST) — we start
+		// and immediately close a listener so the port is known-closed.
+		ln2, err := net.Listen("tcp", "127.0.0.1:0")
+		if err != nil {
+			t.Fatalf("setup: %v", err)
+		}
+		h2, p2str, _ := net.SplitHostPort(ln2.Addr().String())
+		ln2.Close() // now nothing listens — connections get refused
+		p2 := 0
+		fmt.Sscanf(p2str, "%d", &p2)
+
+		cfg := SMTPConfig{
+			Host:    h2,
+			Port:    p2,
+			TLSMode: "",
+		}
+		_, connErr := SMTPConnect(cfg)
+		if connErr == nil {
+			t.Error("expected error for refused connection, got nil")
+		}
+	})
+}
diff --git a/functions/infra/smtp_send_test.go b/functions/infra/smtp_send_test.go
new file mode 100644
index 00000000..215cc01e
--- /dev/null
+++ b/functions/infra/smtp_send_test.go
@@ -0,0 +1,152 @@
+package infra
+
+import (
+	"fmt"
+	"net"
+	"strings"
+	"testing"
+)
+
+// startMockSMTPForSend starts a mock SMTP server and returns host/port separately.
+func startMockSMTPForSend(t *testing.T) (host string, port int, stop func()) {
+	t.Helper()
+	ln, err := net.Listen("tcp", "127.0.0.1:0")
+	if err != nil {
+		t.Fatalf("mock smtp listen: %v", err)
+	}
+	go func() {
+		for {
+			conn, err := ln.Accept()
+			if err != nil {
+				return
+			}
+			go handleMockSMTP(conn)
+		}
+	}()
+	h, ps, _ := net.SplitHostPort(ln.Addr().String())
+	p := 0
+	fmt.Sscanf(ps, "%d", &p)
+	return h, p, func() { ln.Close() }
+}
+
+
+func TestSMTPSend(t *testing.T) {
+	t.Run("envia mensaje texto plano via mock smtp", func(t *testing.T) {
+		host, port, stop := startMockSMTPForSend(t)
+		defer stop()
+
+		cfg := SMTPConfig{Host: host, Port: port, TLSMode: ""}
+		client, err := SMTPConnect(cfg)
+		if err != nil {
+			t.Fatalf("SMTPConnect: %v", err)
+		}
+		defer client.Quit()
+
+		msg := EmailBuildText("alice@example.com", []string{"bob@example.com"}, "Test", "Hello Bob")
+		if err := SMTPSend(client, msg); err != nil {
+			t.Fatalf("SMTPSend: %v", err)
+		}
+	})
+
+	t.Run("envia mensaje html via mock smtp", func(t *testing.T) {
+		host, port, stop := startMockSMTPForSend(t)
+		defer stop()
+
+		cfg := SMTPConfig{Host: host, Port: port, TLSMode: ""}
+		client, err := SMTPConnect(cfg)
+		if err != nil {
+			t.Fatalf("SMTPConnect: %v", err)
+		}
+		defer client.Quit()
+
+		msg := EmailBuildHTML("alice@example.com", []string{"bob@example.com"}, "HTML Test", "<b>Hello</b>")
+		if err := SMTPSend(client, msg); err != nil {
+			t.Fatalf("SMTPSend: %v", err)
+		}
+	})
+
+	t.Run("envia con adjunto via mock smtp", func(t *testing.T) {
+		host, port, stop := startMockSMTPForSend(t)
+		defer stop()
+
+		cfg := SMTPConfig{Host: host, Port: port, TLSMode: ""}
+		client, err := SMTPConnect(cfg)
+		if err != nil {
+			t.Fatalf("SMTPConnect: %v", err)
+		}
+		defer client.Quit()
+
+		msg := EmailBuildText("alice@example.com", []string{"bob@example.com"}, "Att Test", "See attachment")
+		att := EmailAttachment{Filename: "data.txt", ContentType: "text/plain", Data: []byte("file content")}
+		msg = EmailWithAttachment(msg, att)
+
+		if err := SMTPSend(client, msg); err != nil {
+			t.Fatalf("SMTPSend with attachment: %v", err)
+		}
+	})
+}
+
+// TestExtractAddr tests the internal extractAddr helper.
+func TestExtractAddr(t *testing.T) {
+	cases := []struct {
+		input string
+		want  string
+	}{
+		{"Alice <alice@example.com>", "alice@example.com"},
+		{"bob@example.com", "bob@example.com"},
+		{"  carol@example.com  ", "carol@example.com"},
+	}
+	for _, c := range cases {
+		got := extractAddr(c.input)
+		if got != c.want {
+			t.Errorf("extractAddr(%q) = %q, want %q", c.input, got, c.want)
+		}
+	}
+}
+
+// TestBuildMIME tests the MIME builder with different body combinations.
+func TestBuildMIME(t *testing.T) {
+	t.Run("solo texto plano", func(t *testing.T) {
+		msg := EmailBuildText("a@a.com", []string{"b@b.com"}, "Subj", "Hello plain")
+		body, err := buildMIME(msg)
+		if err != nil {
+			t.Fatalf("buildMIME: %v", err)
+		}
+		s := string(body)
+		if !strings.Contains(s, "text/plain") {
+			t.Errorf("expected text/plain in MIME, got:\n%s", s)
+		}
+		if !strings.Contains(s, "Hello plain") {
+			t.Errorf("expected body text in MIME, got:\n%s", s)
+		}
+	})
+
+	t.Run("solo html", func(t *testing.T) {
+		msg := EmailBuildHTML("a@a.com", []string{"b@b.com"}, "Subj", "<b>Bold</b>")
+		body, err := buildMIME(msg)
+		if err != nil {
+			t.Fatalf("buildMIME: %v", err)
+		}
+		s := string(body)
+		if !strings.Contains(s, "text/html") {
+			t.Errorf("expected text/html in MIME, got:\n%s", s)
+		}
+	})
+
+	t.Run("multipart con adjunto", func(t *testing.T) {
+		msg := EmailBuildText("a@a.com", []string{"b@b.com"}, "Subj", "body")
+		att := EmailAttachment{Filename: "f.pdf", ContentType: "application/pdf", Data: []byte("pdf")}
+		msg = EmailWithAttachment(msg, att)
+		body, err := buildMIME(msg)
+		if err != nil {
+			t.Fatalf("buildMIME: %v", err)
+		}
+		s := string(body)
+		if !strings.Contains(s, "multipart/mixed") {
+			t.Errorf("expected multipart/mixed in MIME, got:\n%s", s)
+		}
+		if !strings.Contains(s, "f.pdf") {
+			t.Errorf("expected attachment filename in MIME, got:\n%s", s)
+		}
+	})
+}