diff --git a/dev/Common/File.js b/dev/Common/File.js
index 532f9ffb22..841554056b 100644
--- a/dev/Common/File.js
+++ b/dev/Common/File.js
@@ -138,7 +138,7 @@ export const FileInfo = {
 	getContentType: fileName => {
 		fileName = lowerCase(fileName);
 		if ('winmail.dat' === fileName) {
-			return app + 'ms-tnef';
+			return app + 'vnd.ms-tnef';
 		}
 		let ext = fileName.split('.').pop();
 		if (/^(txt|text|def|list|in|ini|log|sql|cfg|conf)$/.test(ext))
diff --git a/snappymail/v/0.0.0/app/libraries/snappymail/file/mimetype.php b/snappymail/v/0.0.0/app/libraries/snappymail/file/mimetype.php
index e64b57293f..62f1867374 100644
--- a/snappymail/v/0.0.0/app/libraries/snappymail/file/mimetype.php
+++ b/snappymail/v/0.0.0/app/libraries/snappymail/file/mimetype.php
@@ -103,7 +103,7 @@ public static function fromFilename(string $filename) : ?string
 	{
 		$filename = \strtolower($filename);
 		if ('winmail.dat' === $filename) {
-			return 'application/ms-tnef';
+			return static::$types['tnef'];
 		}
 		$extension = \explode('.', $filename);
 		$extension = \array_pop($extension);
@@ -116,7 +116,7 @@ public static function fromFilename(string $filename) : ?string
 	public static function toExtension(string $mime, bool $include_dot = true) : ?string
 	{
 		$mime = \strtolower($mime);
-		if ('application/pgp-signature' == $mime || 'application/pgp-keys' == $mime) {
+		if ('application/pgp-signature' === $mime || 'application/pgp-keys' === $mime) {
 			$ext = 'asc';
 		} else {
 			$mime = \str_replace('application/x-tar', 'application/gtar', $mime);
@@ -149,7 +149,6 @@ public static function toExtension(string $mime, bool $include_dot = true) : ?st
 		'epub' => 'application/epub',
 		'exe' => 'application/x-msdownload',
 		'gz' => 'application/gzip',
-		'gz' => 'application/x-gzip',
 		'hlp' => 'application/winhlp',
 		'js' => 'application/javascript',
 		'json' => 'application/json',
@@ -178,7 +177,9 @@ public static function toExtension(string $mime, bool $include_dot = true) : ?st
 		'swf' => 'application/x-shockwave-flash',
 		'tar' => 'application/gtar',
 //		'tar' => 'application/x-tar',
-//		'tgz' => 'application/x-gzip',
+//		'tgz' => 'application/gzip',
+		'tnef' => 'application/vnd.ms-tnef',
+//		'tnef' => 'application/ms-tnef', // not IANA official
 		'torrent' => 'application/x-bittorrent',
 		'wgt' => 'application/widget',
 		'xls' => 'application/vnd.ms-excel',
diff --git a/snappymail/v/0.0.0/app/libraries/snappymail/stream/tar.php b/snappymail/v/0.0.0/app/libraries/snappymail/stream/tar.php
index f3a124f216..a64c87586e 100644
--- a/snappymail/v/0.0.0/app/libraries/snappymail/stream/tar.php
+++ b/snappymail/v/0.0.0/app/libraries/snappymail/stream/tar.php
@@ -53,7 +53,7 @@ public function pushHttpHeaders(string $name) : void
 			$name .= '.tgz';
 			$name = \preg_match('#^[\x01-\x7F]*$#D', $name) ? $name : '=?UTF-8?B?'.\base64_encode($name).'?=';
 			\header("Content-Disposition: attachment; filename={$name}");
-			\header("Content-Type: application/x-gzip; name={$name}");
+			\header("Content-Type: application/gzip; name={$name}");
 		} else {
 			$name .= '.tar';
 			$name = \preg_match('#^[\x01-\x7F]*$#D', $name) ? $name : '=?UTF-8?B?'.\base64_encode($name).'?=';