diff --git a/cmd/expiration-mailer/main.go b/cmd/expiration-mailer/main.go
index bf56aea75..e9b976729 100644
--- a/cmd/expiration-mailer/main.go
+++ b/cmd/expiration-mailer/main.go
@@ -19,6 +19,7 @@ import (
 	"github.com/letsencrypt/boulder/Godeps/_workspace/src/github.com/codegangsta/cli"
 	"github.com/letsencrypt/boulder/Godeps/_workspace/src/github.com/jmhodges/clock"
 	"github.com/letsencrypt/boulder/Godeps/_workspace/src/gopkg.in/gorp.v1"
+
 	"github.com/letsencrypt/boulder/cmd"
 	"github.com/letsencrypt/boulder/core"
 	blog "github.com/letsencrypt/boulder/log"
@@ -72,7 +73,7 @@ func (m *mailer) sendNags(parsedCert *x509.Certificate, contacts []*core.AcmeURL
 			return err
 		}
 		startSending := m.clk.Now()
-		err = m.mailer.SendMail(emails, msgBuf.String())
+		err = m.mailer.SendMail(emails, "Certificate expiration notice", msgBuf.String())
 		if err != nil {
 			m.stats.Inc("Mailer.Expiration.Errors.SendingNag.SendFailure", 1, 1.0)
 			return err
diff --git a/cmd/expiration-mailer/main_test.go b/cmd/expiration-mailer/main_test.go
index 26ac81c17..d0a83576c 100644
--- a/cmd/expiration-mailer/main_test.go
+++ b/cmd/expiration-mailer/main_test.go
@@ -50,7 +50,7 @@ func (m *mockMail) Clear() {
 	m.Messages = []string{}
 }
 
-func (m *mockMail) SendMail(to []string, msg string) (err error) {
+func (m *mockMail) SendMail(to []string, subject, msg string) (err error) {
 	for range to {
 		m.Messages = append(m.Messages, msg)
 	}
diff --git a/mail/mailer.go b/mail/mailer.go
index dc3a6b366..094583c41 100644
--- a/mail/mailer.go
+++ b/mail/mailer.go
@@ -6,13 +6,17 @@
 package mail
 
 import (
+	"fmt"
+	"math/rand"
 	"net"
 	"net/smtp"
+	"strings"
+	"time"
 )
 
 // Mailer provides the interface for a mailer
 type Mailer interface {
-	SendMail([]string, string) error
+	SendMail([]string, string, string) error
 }
 
 // MailerImpl defines a mail transfer agent to use for sending mail
@@ -35,9 +39,26 @@ func New(server, port, username, password string) MailerImpl {
 	}
 }
 
+func (m *MailerImpl) generateMessage(to []string, subject, body string) []byte {
+	now := time.Now().UTC()
+	headers := []string{
+		fmt.Sprintf("To: %s", strings.Join(to, ", ")),
+		fmt.Sprintf("From: %s", m.From),
+		fmt.Sprintf("Subject: %s", subject),
+		fmt.Sprintf("Date: %s", now.Format("Mon Jan 2 2006 15:04:05 -0700")),
+		fmt.Sprintf("Message-Id: <%s.%d.%s>", now.Format("20060102T150405"), rand.Int63(), m.From),
+	}
+	return []byte(fmt.Sprintf("%s\r\n\r\n%s\r\n", strings.Join(headers, "\r\n"), body))
+}
+
 // SendMail sends an email to the provided list of recipients. The email body
 // is simple text.
-func (m *MailerImpl) SendMail(to []string, msg string) (err error) {
-	err = smtp.SendMail(net.JoinHostPort(m.Server, m.Port), m.Auth, m.From, to, []byte(msg))
-	return
+func (m *MailerImpl) SendMail(to []string, subject, msg string) error {
+	return smtp.SendMail(
+		net.JoinHostPort(m.Server, m.Port),
+		m.Auth,
+		m.From,
+		to,
+		m.generateMessage(to, subject, msg),
+	)
 }