diff --git a/htdocs/core/class/CMailFile.class.php b/htdocs/core/class/CMailFile.class.php
index cd9e47f8a7898136c44d0f298af45a7b1e78a8f1..db9bf8e1ad0b32d4b87388d2d43a554c0182b3dd 100644
--- a/htdocs/core/class/CMailFile.class.php
+++ b/htdocs/core/class/CMailFile.class.php
@@ -680,7 +680,7 @@ class CMailFile
 		global $conf;
 		$out = "";
 
-		$host = dol_getprefix();
+		$host = dol_getprefix('email');
 
 		// Sender
 		//$out.= "Sender: ".getValidAddress($this->addr_from,2)).$this->eol2;
diff --git a/htdocs/core/class/smtps.class.php b/htdocs/core/class/smtps.class.php
index a46672443ac26878c5d76e66bbc1e0abaf183402..6731b46fe0fd516f6fa16047c05ea4a2aac54473 100644
--- a/htdocs/core/class/smtps.class.php
+++ b/htdocs/core/class/smtps.class.php
@@ -1126,7 +1126,7 @@ class SMTPs
 		$host=preg_replace('@tcp://@i','',$host);	// Remove prefix
 		$host=preg_replace('@ssl://@i','',$host);	// Remove prefix
 
-		$host=dol_getprefix().'-'.$host;
+		$host=dol_getprefix('email').'-'.$host;
 		
 		//NOTE: Message-ID should probably contain the username of the user who sent the msg
 		$_header .= 'Subject: '    . $this->getSubject()     . "\r\n";
diff --git a/htdocs/core/lib/functions.lib.php b/htdocs/core/lib/functions.lib.php
index bce67604ee7911c5710b410557b1ed7e2ad7e699..8c810b76b9781c78dfd84b92f2fed9fdd80e518b 100644
--- a/htdocs/core/lib/functions.lib.php
+++ b/htdocs/core/lib/functions.lib.php
@@ -286,19 +286,22 @@ function GETPOST($paramname,$check='',$method=0,$filter=NULL,$options=NULL)
  *  This prefix is unique for instance and avoid conflict between multi-instances,
  *  even when having two instances with one root dir or two instances in virtual servers
  *
+ *  @param  string  $mode       '' or 'email'              
  *  @return	string      		A calculated prefix
  */
-function dol_getprefix()
+function dol_getprefix($mode='')
 {
     global $conf;
     
+    // If MAIL_PREFIX_FOR_EMAIL_ID is set and prefix is for email
+    if ($mode == 'email' && ! empty($conf->global->MAIL_PREFIX_FOR_EMAIL_ID))
+    {
+        if ($conf->global->MAIL_PREFIX_FOR_EMAIL_ID != 'SERVER_NAME') return $conf->global->MAIL_PREFIX_FOR_EMAIL_ID;
+        else if (isset($_SERVER["SERVER_NAME"])) return $_SERVER["SERVER_NAME"];
+    }
+
 	if (isset($_SERVER["SERVER_NAME"]) && isset($_SERVER["DOCUMENT_ROOT"]))
 	{
-	    if (! empty($conf->global->MAIL_PREFIX_FOR_EMAIL_ID))
-	    {
-	        if ($conf->global->MAIL_PREFIX_FOR_EMAIL_ID == 'SERVER_NAME') return $_SERVER["SERVER_NAME"];
-	        return $conf->global->MAIL_PREFIX_FOR_EMAIL_ID;
-	    }
 		return dol_hash($_SERVER["SERVER_NAME"].$_SERVER["DOCUMENT_ROOT"].DOL_DOCUMENT_ROOT.DOL_URL_ROOT);
 		// Use this for a "clear" cookie name
 		//return dol_sanitizeFileName($_SERVER["SERVER_NAME"].$_SERVER["DOCUMENT_ROOT"].DOL_DOCUMENT_ROOT.DOL_URL_ROOT);