diff --git a/mail/mailer.go b/mail/mailer.go
index 1c9a85359..ec7680cfd 100644
--- a/mail/mailer.go
+++ b/mail/mailer.go
@@ -13,6 +13,7 @@ import (
 	"net"
 	"net/mail"
 	"net/smtp"
+	"net/textproto"
 	"strconv"
 	"strings"
 	"time"
@@ -151,7 +152,7 @@ func (m *MailerImpl) generateMessage(to []string, subject, body string) ([]byte,
 	addrs := []string{}
 	for _, a := range to {
 		if !core.IsASCII(a) {
-			return nil, fmt.Errorf("Non-ASCII email address")
+			return nil, fmt.Errorf("Non-ASCIR email address")
 		}
 		addrs = append(addrs, strconv.Quote(a))
 	}
@@ -292,10 +293,31 @@ func (m *MailerImpl) SendMail(to []string, subject, msg string) error {
 			m.stats.Inc("SendMail.Reconnects", 1)
 			continue
 		} else if err != nil {
-			// If it wasn't an EOF error it is unexpected and we return from
-			// SendMail() with an error
-			m.stats.Inc("SendMail.Errors", 1)
-			return err
+			/*
+			 *  If the error is an instace of `textproto.Error` with a SMTP error code,
+			 *  and that error code is 421 then treat this as a reconnect-able event.
+			 *
+			 *  The SMTP RFC defines this error code as:
+			 *   421 <domain> Service not available, closing transmission channel
+			 *   (This may be a reply to any command if the service knows it
+			 *   must shut down)
+			 *
+			 * In practice we see this code being used by our production SMTP server
+			 * when the connection has gone idle for too long. For more information
+			 * see issue #2249[0].
+			 *
+			 * [0] - https://github.com/letsencrypt/boulder/issues/2249
+			 */
+			if protoErr, ok := err.(*textproto.Error); ok && protoErr.Code == 421 {
+				m.stats.Inc("SendMail.Errors.SMTP.421", 1)
+				m.reconnect()
+				m.stats.Inc("SendMail.Reconnects", 1)
+			} else {
+				// If it wasn't an EOF error or a SMTP 421 it is unexpected and we
+				// return from SendMail() with an error
+				m.stats.Inc("SendMail.Errors", 1)
+				return err
+			}
 		}
 	}
 
diff --git a/test/mail-test-srv/main.go b/test/mail-test-srv/main.go
index 3044889f3..a72c6723d 100644
--- a/test/mail-test-srv/main.go
+++ b/test/mail-test-srv/main.go
@@ -101,11 +101,25 @@ func (srv *mailSrv) handleConn(conn net.Conn) {
 		case "MAIL":
 			srv.connNumberMutex.RLock()
 			if srv.connNumber <= srv.closeFirst {
-				log.Printf(
-					"mail-test-srv: connection # %d < -closeFirst parameter %d, disconnecting client. Bye!\n",
-					srv.connNumber, srv.closeFirst)
-				clearState()
-				conn.Close()
+				// Half of the time, close cleanly to simulate the server side closing
+				// unexpectedly.
+				if srv.connNumber%2 == 0 {
+					log.Printf(
+						"mail-test-srv: connection # %d < -closeFirst parameter %d, disconnecting client. Bye!\n",
+						srv.connNumber, srv.closeFirst)
+					clearState()
+					conn.Close()
+				} else {
+					// The rest of the time, simulate a stale connection timeout by sending
+					// a SMTP 421 message. This replicates the timeout/close from issue
+					// 2249 - https://github.com/letsencrypt/boulder/issues/2249
+					log.Printf(
+						"mail-test-srv: connection # %d < -closeFirst parameter %d, disconnecting with 421. Bye!\n",
+						srv.connNumber, srv.closeFirst)
+					clearState()
+					conn.Write([]byte("421 1.2.3 foo.bar.baz Error: timeout exceeded \r\n"))
+					conn.Close()
+				}
 			}
 			srv.connNumberMutex.RUnlock()
 			clearState()