Feature/Allow special characters in email regex pattern

consts.go

@@ -53,7 +53,8 @@ const (
 	// Regex patterns
 	availableCmdsRegexPattern  = `(?i)helo|ehlo|mail from:|rcpt to:|data|rset|noop|quit`
 	domainRegexPattern         = `(?i)([\p{L}0-9]+([\-.]{1}[\p{L}0-9]+)*\.\p{L}{2,63}|localhost)`
-	emailRegexPattern          = `(?i)(?:[\p{L}\p{N}\s]*?<?)*?([a-zA-Z0-9][-a-zA-Z0-9.]*[a-zA-Z0-9]@` + domainRegexPattern + `)>*`
+	localPartChars             = `[a-zA-Z0-9.!#$%&'*+\-/=?^_\x60{|}~]`
+	emailRegexPattern          = `(?i)(?:[\p{L}\p{N}\s]*?<?)*?(` + localPartChars + `+(?:\.` + localPartChars + `+)*@` + domainRegexPattern + `)>*`
 	ipAddressRegexPattern      = `(\b25[0-5]|\b2[0-4][0-9]|\b[01]?[0-9][0-9]?)(\.(25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)){3}`
 	addressLiteralRegexPattern = `|\[` + ipAddressRegexPattern + `\]`
 

handler_mailfrom_test.go

@@ -260,16 +260,26 @@ func TestHandlerMailfromMailfromEmail(t *testing.T) {
 		assert.Equal(t, emptyString, handler.mailfromEmail("MAIL FROM: "+invalidEmail))
 	})
 
-	t.Run("when request includes invalid email starting with dot", func(t *testing.T) {
-		invalidEmail := "[email protected]"
+	t.Run("when request includes email with plus sign", func(t *testing.T) {
+		email := "[email protected]"
+		assert.Equal(t, email, handler.mailfromEmail("MAIL FROM: "+email))
+	})
 
-		assert.Equal(t, emptyString, handler.mailfromEmail("MAIL FROM: "+invalidEmail))
+	t.Run("when request includes email with multiple special characters", func(t *testing.T) {
+		email := "user.name+tag!#$%@example.com"
+		assert.Equal(t, email, handler.mailfromEmail("MAIL FROM: "+email))
 	})
 
-	t.Run("when request includes invalid email ending with dot before @", func(t *testing.T) {
-		invalidEmail := "[email protected]"
+	t.Run("when request includes email with special characters and angle brackets", func(t *testing.T) {
+		rawEmail := "[email protected]"
+		request := "MAIL FROM: <" + rawEmail + ">"
+		assert.Equal(t, rawEmail, handler.mailfromEmail(request))
+	})
 
-		assert.Equal(t, emptyString, handler.mailfromEmail("MAIL FROM: "+invalidEmail))
+	t.Run("when request includes email with special characters and display name", func(t *testing.T) {
+		rawEmail := "[email protected]"
+		request := "MAIL FROM: Support Team <" + rawEmail + ">"
+		assert.Equal(t, rawEmail, handler.mailfromEmail(request))
 	})
 }
 

handler_rcptto_test.go

@@ -359,18 +359,6 @@ func TestHandlerRcpttoRcpttoEmail(t *testing.T) {
 
 		assert.Equal(t, emptyString, handler.rcpttoEmail("RCPT TO: "+invalidEmail))
 	})
-
-	t.Run("when request includes invalid email starting with dot", func(t *testing.T) {
-		invalidEmail := "[email protected]"
-
-		assert.Equal(t, emptyString, handler.rcpttoEmail("RCPT TO: "+invalidEmail))
-	})
-
-	t.Run("when request includes invalid email ending with dot before @", func(t *testing.T) {
-		invalidEmail := "[email protected]"
-
-		assert.Equal(t, emptyString, handler.rcpttoEmail("RCPT TO: "+invalidEmail))
-	})
 }
 
 func TestHandlerRcpttoIsBlacklistedEmail(t *testing.T) {