diff --git a/htdocs/core/actions_massactions.inc.php b/htdocs/core/actions_massactions.inc.php
index 5fbc305b58bf0..3ef0b96c1e846 100644
--- a/htdocs/core/actions_massactions.inc.php
+++ b/htdocs/core/actions_massactions.inc.php
@@ -88,9 +88,10 @@
 	$oneemailperrecipient = (GETPOST('oneemailperrecipient', 'int') ? 1 : 0);
 
 	if (!$error) {
-		$thirdparty = new Societe($db);
-
 		$objecttmp = new $objectclass($db);
+
+		// Define object $thirdparty (Societe or User, Adherent, ConferenceOrBoothAttendee...)
+		$thirdparty = new Societe($db);
 		if ($objecttmp->element == 'expensereport') {
 			$thirdparty = new User($db);
 		}
@@ -100,28 +101,33 @@
 		if ($objecttmp->element == 'holiday') {
 			$thirdparty = new User($db);
 		}
+		if ($objecttmp->element == 'conferenceorboothattendee') {
+			$thirdparty = new ConferenceOrBoothAttendee($db);
+		}
 
 		foreach ($toselect as $toselectid) {
 			$objecttmp = new $objectclass($db); // we must create new instance because instance is saved into $listofobjectref array for future use
 			$result = $objecttmp->fetch($toselectid);
 			if ($result > 0) {
 				$listofobjectid[$toselectid] = $toselectid;
-
-				$thirdpartyid = ($objecttmp->fk_soc ? $objecttmp->fk_soc : $objecttmp->socid);
+				$tmpobjectid = ($objecttmp->fk_soc ? $objecttmp->fk_soc : $objecttmp->socid);
 				if ($objecttmp->element == 'societe') {
-					$thirdpartyid = $objecttmp->id;
+					$tmpobjectid = $objecttmp->id;
 				}
 				if ($objecttmp->element == 'expensereport') {
-					$thirdpartyid = $objecttmp->fk_user_author;
+					$tmpobjectid = $objecttmp->fk_user_author;
 				}
 				if ($objecttmp->element == 'partnership' && getDolGlobalString('PARTNERSHIP_IS_MANAGED_FOR') == 'member') {
-					$thirdpartyid = $objecttmp->fk_member;
+					$tmpobjectid = $objecttmp->fk_member;
 				}
 				if ($objecttmp->element == 'holiday') {
-					$thirdpartyid = $objecttmp->fk_user;
+					$tmpobjectid = $objecttmp->fk_user;
 				}
-				if (empty($thirdpartyid)) {
-					$thirdpartyid = 0;
+				if ($objecttmp->element == 'conferenceorboothattendee') {
+					$tmpobjectid = $objecttmp->id;
+				}
+				if (empty($tmpobjectid)) {
+					$tmpobjectid = 0;
 				}
 
 				if ($objectclass == 'Facture') {
@@ -142,8 +148,8 @@
 					}
 				}
 
-				$listofobjectthirdparties[$thirdpartyid] = $thirdpartyid;
-				$listofobjectref[$thirdpartyid][$toselectid] = $objecttmp;
+				$listofobjectthirdparties[$tmpobjectid] = $tmpobjectid;
+				$listofobjectref[$tmpobjectid][$toselectid] = $objecttmp;
 			}
 		}
 	}
@@ -175,7 +181,7 @@
 		$massaction = 'presend';
 	}
 
-	// Loop on each recipient/thirdparty
+	// Loop on each recipient (may be a thirdparty but also a user, a conferenceorboothattendee, ...)
 	if (!$error) {
 		foreach ($listofobjectthirdparties as $thirdpartyid) {
 			$result = $thirdparty->fetch($thirdpartyid);
@@ -187,7 +193,7 @@
 			$sendto = '';
 			$sendtocc = '';
 			$sendtobcc = '';
-			$sendtoid = array();
+			//$sendtoid = array();
 
 			// Define $sendto
 			$tmparray = array();
@@ -202,7 +208,7 @@
 						$tmparray[] = $thirdparty->name.' <'.$thirdparty->email.'>';
 					} elseif ($val && method_exists($thirdparty, 'contact_get_property')) {		// Id of contact
 						$tmparray[] = $thirdparty->contact_get_property((int) $val, 'email');
-						$sendtoid[] = $val;
+						//$sendtoid[] = $val;
 					}
 				}
 			}
@@ -302,6 +308,8 @@
 						if (count($emails_to_sends) > 0) {
 							$sendto = implode(',', $emails_to_sends);
 						}
+					} elseif ($objectobj->element == 'conferenceorboothattendee') {
+						$sendto = $objectobj->email;
 					} else {
 						$objectobj->fetch_thirdparty();
 						$sendto = $objectobj->thirdparty->email;
diff --git a/htdocs/core/class/html.formmail.class.php b/htdocs/core/class/html.formmail.class.php
index 665ec68c85fde..5a03184996488 100644
--- a/htdocs/core/class/html.formmail.class.php
+++ b/htdocs/core/class/html.formmail.class.php
@@ -543,6 +543,10 @@ public function get_form($addfileaction = 'addfile', $removefileaction = 'remove
 				$helpforsubstitution .= $langs->trans('AvailableVariables').' :<br>'."\n";
 			}
 			foreach ($this->substit as $key => $val) {
+				// Do not show deprecated variables into the tooltip help of substitution variables
+				if (in_array($key, array('__NEWREF__', '__REFCLIENT__', '__REFSUPPLIER__', '__SUPPLIER_ORDER_DATE_DELIVERY__', '__SUPPLIER_ORDER_DELAY_DELIVERY__'))) {
+					continue;
+				}
 				$helpforsubstitution .= $key.' -> '.$langs->trans(dol_string_nohtmltag(dolGetFirstLineOfText($val))).'<br>';
 			}
 			if (!empty($this->withsubstit)) {	// Unset or set ->withsubstit=0 to disable this.
diff --git a/htdocs/core/lib/functions.lib.php b/htdocs/core/lib/functions.lib.php
index 7a6bb97c0f905..03783e37561d8 100644
--- a/htdocs/core/lib/functions.lib.php
+++ b/htdocs/core/lib/functions.lib.php
@@ -7747,7 +7747,7 @@ function getCommonSubstitutionArray($outputlangs, $onlykey = 0, $exclude = null,
 			$substitutionarray['__DATE_DELIVERY_MM__'] = (isset($object->date_livraison) ? dol_print_date($object->date_livraison, "%M") : '');
 			$substitutionarray['__DATE_DELIVERY_SS__'] = (isset($object->date_livraison) ? dol_print_date($object->date_livraison, "%S") : '');
 
-			// For backward compatibility
+			// For backward compatibility (deprecated)
 			$substitutionarray['__REFCLIENT__'] = (isset($object->ref_client) ? $object->ref_client : (isset($object->ref_customer) ? $object->ref_customer : null));
 			$substitutionarray['__REFSUPPLIER__'] = (isset($object->ref_supplier) ? $object->ref_supplier : null);
 			$substitutionarray['__SUPPLIER_ORDER_DATE_DELIVERY__'] = (isset($object->date_livraison) ? dol_print_date($object->date_livraison, 'day', 0, $outputlangs) : '');
@@ -7841,6 +7841,11 @@ function getCommonSubstitutionArray($outputlangs, $onlykey = 0, $exclude = null,
 				$substitutionarray['__CANDIDATE_FIRSTNAME__'] = isset($object->firstname) ? $object->firstname : '';
 				$substitutionarray['__CANDIDATE_LASTNAME__'] = isset($object->lastname) ? $object->lastname : '';
 			}
+			if (is_object($object) && $object->element == 'conferenceorboothattendee') {
+				$substitutionarray['__ATTENDEE_FULLNAME__'] = $object->getFullName($outputlangs);
+				$substitutionarray['__ATTENDEE_FIRSTNAME__'] = isset($object->firstname) ? $object->firstname : '';
+				$substitutionarray['__ATTENDEE_LASTNAME__'] = isset($object->lastname) ? $object->lastname : '';
+			}
 
 			if (is_object($object->project)) {
 				$substitutionarray['__PROJECT_ID__'] = (is_object($object->project) ? $object->project->id : '');