Check for mbstring before trying to use it in parseAddresses

changelog.md

@@ -1,5 +1,8 @@
 # PHPMailer Change Log
 
+## WIP
+* Check for mbstring extension before decoding addresss in `parseAddress`
+
 ## Version 6.3.0 (February 19th, 2021)
 * Handle early connection errors such as 421 during connection and EHLO states
 * Switch to Github Actions for CI

composer.json

@@ -40,7 +40,7 @@
         "yoast/phpunit-polyfills": "^0.2.0"
     },
     "suggest": {
-        "ext-mbstring": "Needed to send email in multibyte encoding charset",
+        "ext-mbstring": "Needed to send email in multibyte encoding charset or decode encoded addresses",
         "hayageek/oauth2-yahoo": "Needed for Yahoo XOAUTH2 authentication",
         "league/oauth2-google": "Needed for Google XOAUTH2 authentication",
         "psr/log": "For optional PSR-3 debug logging",

src/PHPMailer.php

@@ -1199,7 +1199,7 @@ class PHPMailer
                     )
                 ) {
                     //Decode the name part if it's present and encoded
-                    if (property_exists($address, 'personal') && preg_match('/^=\?.*\?=$/', $address->personal)) {
+                    if (extension_loaded('mbstring') && property_exists($address, 'personal') && preg_match('/^=\?.*\?=$/', $address->personal)) {
                         $address->personal = mb_decode_mimeheader($address->personal);
                     }