Fix domain name pattern in email regex (#6739)

Fixes #6735

modules/markup/html.go

@@ -63,7 +63,7 @@ var (
 	// well as the HTML5 spec:
 	//   http://spec.commonmark.org/0.28/#email-address
 	//   https://html.spec.whatwg.org/multipage/input.html#e-mail-state-(type%3Demail)
-	emailRegex = regexp.MustCompile("(?:\\s|^|\\(|\\[)([a-zA-Z0-9.!#$%&'*+\\/=?^_`{|}~-]+@[a-zA-Z0-9](?:[a-zA-Z0-9-]{0,61}[a-zA-Z0-9])?(?:\\.[a-zA-Z0-9](?:[a-zA-Z0-9-]{0,61}[a-zA-Z0-9])?)*)(?:\\s|$|\\)|\\]|\\.(\\s|$))")
+	emailRegex = regexp.MustCompile("(?:\\s|^|\\(|\\[)([a-zA-Z0-9.!#$%&'*+\\/=?^_`{|}~-]+@[a-zA-Z0-9](?:[a-zA-Z0-9-]{0,61}[a-zA-Z0-9])?(?:\\.[a-zA-Z0-9]{2,}(?:[a-zA-Z0-9-]{0,61}[a-zA-Z0-9])?)+)(?:\\s|$|\\)|\\]|\\.(\\s|$))")
 
 	linkRegex, _ = xurls.StrictMatchingScheme("https?://")
 )

modules/markup/html_test.go

@@ -176,6 +176,9 @@ func TestRender_email(t *testing.T) {
 	test(
 		"info@gitea.com.",
 		`<p><a href="mailto:info@gitea.com" rel="nofollow">info@gitea.com</a>.</p>`)
+	test(
+		"firstname+lastname@gitea.com",
+		`<p><a href="mailto:firstname+lastname@gitea.com" rel="nofollow">firstname+lastname@gitea.com</a></p>`)
 	test(
 		"send email to info@gitea.co.uk.",
 		`<p>send email to <a href="mailto:info@gitea.co.uk" rel="nofollow">info@gitea.co.uk</a>.</p>`)
@@ -190,6 +193,18 @@ func TestRender_email(t *testing.T) {
 	test(
 		"git@try.gitea.io:go-gitea/gitea.git",
 		`<p>git@try.gitea.io:go-gitea/gitea.git</p>`)
+	test(
+		"gitea@3",
+		`<p>gitea@3</p>`)
+	test(
+		"gitea@gmail.c",
+		`<p>gitea@gmail.c</p>`)
+	test(
+		"email@domain@domain.com",
+		`<p>email@domain@domain.com</p>`)
+	test(
+		"email@domain..com",
+		`<p>email@domain..com</p>`)
 }
 
 func TestRender_ShortLinks(t *testing.T) {