diff --git a/src/ESP_Mail_Client.cpp b/src/ESP_Mail_Client.cpp
index d76b0492..ab5ba1ec 100644
--- a/src/ESP_Mail_Client.cpp
+++ b/src/ESP_Mail_Client.cpp
@@ -767,7 +767,8 @@ void ESP_Mail_Client::splitToken(const char *str, MB_VECTOR<MB_String> &tk, cons
   MB_String tmp;
   while (pp != NULL)
   {
-    strsep(&end, delim);
+     // See RFC2047.h
+    ESP_MAIL_STRSEP(&end, delim);
     if (strlen(pp) > 0)
     {
       tmp = pp;
diff --git a/src/ESP_Mail_IMAP.h b/src/ESP_Mail_IMAP.h
index 29629fca..4a119227 100644
--- a/src/ESP_Mail_IMAP.h
+++ b/src/ESP_Mail_IMAP.h
@@ -3658,7 +3658,8 @@ void ESP_Mail_Client::parseFoldersResponse(IMAPSession *imap, char *buf, bool li
 
         while (pp != NULL)
         {
-            strsep(&end, " ");
+            // See RFC2047.h
+            ESP_MAIL_STRSEP(&end, " ");
             count++;
 
             if (count >= tkPos && strlen(pp) > 0)
@@ -3923,7 +3924,8 @@ bool ESP_Mail_Client::getFlags(IMAPSession *imap, char *buf, esp_mail_imap_respo
 
         while (pp != NULL)
         {
-            strsep(&end, " ");
+             // See RFC2047.h
+            ESP_MAIL_STRSEP(&end, " ");
             count++;
             if (count >= tkPos && strlen(pp) > 0)
             {
diff --git a/src/extras/Networks_Provider.h b/src/extras/Networks_Provider.h
index 9add6247..fb731594 100644
--- a/src/extras/Networks_Provider.h
+++ b/src/extras/Networks_Provider.h
@@ -10,6 +10,8 @@
 
 #include "SDK_Version_Common.h"
 
+#define ESP_MAIL_STRSEP strsep
+
 #if defined(ESP32) || defined(ESP8266) || defined(ARDUINO_RASPBERRY_PI_PICO_W) || __has_include(<WiFiNINA.h>) ||__has_include(<WiFi101.h>) || __has_include(<WiFiS3.h>)
 
 #if !defined(ESP_MAIL_DISABLE_ONBOARD_WIFI)
@@ -28,6 +30,12 @@
 #include <WiFiS3.h>
 #endif
 
+#if __has_include(<WiFiS3.h>)
+#undef ESP_MAIL_STRSEP
+#define ESP_MAIL_STRSEP strsepImpl
+#define ESP_MAIL_USE_STRSEP_IMPL
+#endif
+
 #if !defined(ARDUINO_RASPBERRY_PI_PICO_W) && !defined(MB_ARDUINO_ARCH_SAMD) && !__has_include(<WiFiS3.h>)
 #define ESP_MAIL_HAS_WIFI_DISCONNECT
 #endif
diff --git a/src/extras/RFC2047.cpp b/src/extras/RFC2047.cpp
index a4e237d3..544b787c 100644
--- a/src/extras/RFC2047.cpp
+++ b/src/extras/RFC2047.cpp
@@ -77,8 +77,8 @@ void RFC2047_Decoder::rfc2047DecodeWord(char *d, const char *s, size_t dlen)
 
   while (pp != NULL)
   {
-
-    strsep(&end, "?");
+    // See RFC2047.h
+    ESP_MAIL_STRSEP(&end, "?");
     count++;
     switch (count)
     {
@@ -153,7 +153,7 @@ void RFC2047_Decoder::rfc2047DecodeWord(char *d, const char *s, size_t dlen)
       }
       break;
     }
-    
+
     pp = end;
   }
 
diff --git a/src/extras/RFC2047.h b/src/extras/RFC2047.h
index ca4b5bdb..58df80aa 100644
--- a/src/extras/RFC2047.h
+++ b/src/extras/RFC2047.h
@@ -11,6 +11,7 @@
 #include <Arduino.h>
 #include "ESP_Mail_FS.h"
 #include "MB_FS.h"
+#include "Networks_Provider.h"
 
 #if defined(ESP32)
 #if defined(BOARD_HAS_PSRAM) && defined(ESP_Mail_USE_PSRAM)
@@ -20,9 +21,9 @@
 
 #define strfcpy(A, B, C) strncpy(A, B, C), *(A + (C)-1) = 0
 
-
-
-static char *__attribute__((used)) strsep(char **stringp, const char *delim)
+#if defined(ESP_MAIL_USE_STRSEP_IMPL)
+// This is strsep implementation because strdup may not available in some platform.
+static char *__attribute__((used)) strsepImpl(char **stringp, const char *delim)
 {
   char *rv = *stringp;
   if (rv)
@@ -36,14 +37,16 @@ static char *__attribute__((used)) strsep(char **stringp, const char *delim)
   return rv;
 }
 
+#endif
+
 enum
 {
-    ENCOTHER,
-    ENC7BIT,
-    ENC8BIT,
-    ENCQUOTEDPRINTABLE,
-    ENCBASE64,
-    ENCBINARY
+  ENCOTHER,
+  ENC7BIT,
+  ENC8BIT,
+  ENCQUOTEDPRINTABLE,
+  ENCBASE64,
+  ENCBINARY
 };
 
 __attribute__((used)) static const char *Charset = "utf-8";
@@ -78,14 +81,14 @@ class RFC2047_Decoder
 {
 
 public:
-    RFC2047_Decoder();
-    ~RFC2047_Decoder();
-    void decode(MB_FS *mbfs, char *d, const char *s, size_t dlen);
+  RFC2047_Decoder();
+  ~RFC2047_Decoder();
+  void decode(MB_FS *mbfs, char *d, const char *s, size_t dlen);
 
 private:
-    void rfc2047DecodeWord(char *d, const char *s, size_t dlen);
-    char *safe_strdup(const char *s);
-    MB_FS *mbfs = nullptr;
+  void rfc2047DecodeWord(char *d, const char *s, size_t dlen);
+  char *safe_strdup(const char *s);
+  MB_FS *mbfs = nullptr;
 };
 
 #endif // RFC2047_H
\ No newline at end of file