diff --git a/e-invoicing-domain/src/main/kotlin/net/codinux/invoicing/mail/MailReader.kt b/e-invoicing-domain/src/main/kotlin/net/codinux/invoicing/mail/MailReader.kt
index c8f69e4..1136df6 100644
--- a/e-invoicing-domain/src/main/kotlin/net/codinux/invoicing/mail/MailReader.kt
+++ b/e-invoicing-domain/src/main/kotlin/net/codinux/invoicing/mail/MailReader.kt
@@ -185,7 +185,7 @@ class MailReader(
      *
      * -> This method removes parameters and return media type (first part) only
      */
-    private fun getMediaType(part: Part): String? = part.contentType?.let { contentType ->
+    private fun getMediaType(part: Part): String? = part.contentType?.lowercase()?.let { contentType ->
         val indexOfSeparator = contentType.indexOf(';')
 
         if (indexOfSeparator > -1) {