diff --git a/server/smtpd/lib.go b/server/smtpd/lib.go
index 0574c50..49f1382 100644
--- a/server/smtpd/lib.go
+++ b/server/smtpd/lib.go
@@ -29,7 +29,9 @@ var (
 	Debug      = false
 	rcptToRE   = regexp.MustCompile(`[Tt][Oo]:\s?<(.+)>`)
 	mailFromRE = regexp.MustCompile(`[Ff][Rr][Oo][Mm]:\s?<(.*)>(\s(.*))?`) // Delivery Status Notifications are sent with "MAIL FROM:<>"
-	mailSizeRE = regexp.MustCompile(`[Ss][Ii][Zz][Ee]=(\d+)`)
+
+	// extract mail size from 'MAIL FROM' parameter
+	mailFromSizeRE = regexp.MustCompile(`(?U)(^| |,)[Ss][Ii][Zz][Ee]=(.*)($|,| )`)
 )
 
 // Handler function called upon successful receipt of an email.
@@ -411,12 +413,13 @@ loop:
 			} else {
 				// Validate the SIZE parameter if one was sent.
 				if len(match[2]) > 0 { // A parameter is present
-					sizeMatch := mailSizeRE.FindStringSubmatch(match[3])
+					sizeMatch := mailFromSizeRE.FindStringSubmatch(match[3])
 					if sizeMatch == nil {
-						s.writef("501 5.5.4 Syntax error in parameters or arguments (invalid SIZE parameter)")
+						// ignore other parameter
+						s.writef("250 2.1.0 Ok")
 					} else {
 						// Enforce the maximum message size if one is set.
-						size, err := strconv.Atoi(sizeMatch[1])
+						size, err := strconv.Atoi(sizeMatch[2])
 						if err != nil { // Bad SIZE parameter
 							s.writef("501 5.5.4 Syntax error in parameters or arguments (invalid SIZE parameter)")
 						} else if s.srv.MaxSize > 0 && size > s.srv.MaxSize { // SIZE above maximum size, if set
diff --git a/server/smtpd/smtpd_test.go b/server/smtpd/smtpd_test.go
index af590d6..6f8cf61 100644
--- a/server/smtpd/smtpd_test.go
+++ b/server/smtpd/smtpd_test.go
@@ -148,11 +148,15 @@ func TestCmdMAIL(t *testing.T) {
 	cmdCode(t, conn, "MAIL FROM:<sender@example.com> SIZE=1000", "250")
 
 	// MAIL with bad size parameter should return 501 syntax error
-	cmdCode(t, conn, "MAIL FROM:<sender@example.com> SIZE", "501")
 	cmdCode(t, conn, "MAIL FROM:<sender@example.com> SIZE=", "501")
 	cmdCode(t, conn, "MAIL FROM:<sender@example.com> SIZE= ", "501")
 	cmdCode(t, conn, "MAIL FROM:<sender@example.com> SIZE=foo", "501")
 
+	// MAIL with options should be ignored except for SIZE
+	cmdCode(t, conn, "MAIL FROM:<sender@example.com> BODY=8BITMIME", "250")           // ignored
+	cmdCode(t, conn, "MAIL FROM:<sender@example.com> BODY=8BITMIME,SIZE=1000", "250") // size detected
+	cmdCode(t, conn, "MAIL FROM:<sender@example.com> BODY=8BITMIME,SIZE=foo", "501")  // ignored
+
 	// TODO: MAIL with valid AUTH parameter should return 250 Ok
 
 	// TODO: MAIL with invalid AUTH parameter must return 501 syntax error
@@ -170,7 +174,6 @@ func TestCmdMAILMaxSize(t *testing.T) {
 	cmdCode(t, conn, "MAIL FROM:<sender@example.com>", "250")
 
 	// MAIL with bad size parameter should return 501 syntax error
-	cmdCode(t, conn, "MAIL FROM:<sender@example.com> SIZE", "501")
 	cmdCode(t, conn, "MAIL FROM:<sender@example.com> SIZE=", "501")
 	cmdCode(t, conn, "MAIL FROM:<sender@example.com> SIZE= ", "501")
 	cmdCode(t, conn, "MAIL FROM:<sender@example.com> SIZE=foo", "501")