diff --git a/htdocs/core/class/smtps.class.php b/htdocs/core/class/smtps.class.php
index c287aae1c2f..dbaaacc2d18 100644
--- a/htdocs/core/class/smtps.class.php
+++ b/htdocs/core/class/smtps.class.php
@@ -464,20 +464,26 @@ class SMTPs
 			$host = 'tls://'.$host;
 		}
 
-		$hosth = $host;
+		$hosth = $host;	// so for example 'localhost' or 'smtp-relay.gmail.com'
 
 		if (!empty($conf->global->MAIL_SMTP_USE_FROM_FOR_HELO)) {
-			// If the from to is 'aaa <bbb@ccc.com>', we will keep 'ccc.com'
-			$hosth = $this->getFrom('addr');
-			$hosth = preg_replace('/^.*</', '', $hosth);
-			$hosth = preg_replace('/>.*$/', '', $hosth);
-			$hosth = preg_replace('/.*@/', '', $hosth);
+			if (!is_numeric($conf->global->MAIL_SMTP_USE_FROM_FOR_HELO)) {
+				// If value of MAIL_SMTP_USE_FROM_FOR_HELO is a string, we use it as domain name
+				$hosth = $conf->global->MAIL_SMTP_USE_FROM_FOR_HELO;
+			} else {
+				// If value of MAIL_SMTP_USE_FROM_FOR_HELO is 1, we use the domain in the from.
+				// So if the from to is 'aaa <bbb@ccc.com>', we will keep 'ccc.com'
+				$hosth = $this->getFrom('addr');
+				$hosth = preg_replace('/^.*</', '', $hosth);
+				$hosth = preg_replace('/>.*$/', '', $hosth);
+				$hosth = preg_replace('/.*@/', '', $hosth);
+			}
 		}
 
 		if ($_retVal = $this->socket_send_str('EHLO '.$hosth, '250')) {
 			if ($usetls) {
 				/*
-				The following dialog illustrates how a client and server can start a TLS STARTTLS session
+				The following dialog illustrates how a client and server can start a TLS STARTTLS session:
 				S: <waits for connection on TCP port 25>
 				C: <opens connection>
 				S: 220 mail.imc.org SMTP service ready
@@ -494,6 +500,39 @@ class SMTPs
 				S: 250-server-domain.com
 				S: 250 AUTH LOGIN
 				C: <continues by sending an SMTP command
+
+				Another example here:
+				S: 220 smtp.server.com Simple Mail Transfer Service Ready
+				C: EHLO client.example.com
+				S: 250-smtp.server.com Hello client.example.com
+				S: 250-SIZE 1000000
+				S: 250-AUTH LOGIN PLAIN CRAM-MD5
+				S: 250-STARTTLS
+				S: 250 HELP
+				C: STARTTLS
+				S: 220 TLS go ahead
+				C: EHLO client.example.com *
+				S: 250-smtp.server.com Hello client.example.com
+				S: 250-SIZE 1000000
+				S: 250-AUTH LOGIN PLAIN CRAM-MD5
+				S: 250 HELP
+				C: AUTH LOGIN
+				S: 334 VXNlcm5hbWU6
+				C: adlxdkej
+				S: 334 UGFzc3dvcmQ6
+				C: lkujsefxlj
+				S: 235 2.7.0 Authentication successful
+				C: MAIL FROM:<mail@samlogic.com>
+				S: 250 OK
+				C: RCPT TO:<john@mail.com>
+				S: 250 OK
+				C: DATA
+				S: 354 Send message, end with a "." on a line by itself
+				C: <The message data (body text, subject, e-mail header, attachments etc) is sent>
+				S .
+				S: 250 OK, message accepted for delivery: queued as 12345
+				C: QUIT
+				S: 221 Bye
 				*/
 				if (!$_retVal = $this->socket_send_str('STARTTLS', 220)) {
 					$this->_setErr(131, 'STARTTLS connection is not supported.');
@@ -517,10 +556,10 @@ class SMTPs
 					$this->_setErr(132, 'STARTTLS connection failed.');
 					return $_retVal;
 				}
-				// Most server servers expect a 2nd pass of EHLO after TLS is established to get another time
+				// Most servers expect a 2nd pass of EHLO after TLS is established to get another time
 				// the answer with list of supported AUTH methods. They may differs between non STARTTLS and with STARTTLS.
-				if (!$_retVal = $this->socket_send_str('EHLO '.$hosth, '250')) {
-					$this->_setErr(126, '"'.$hosth.'" does not support authenticated connections.');
+				if (! $_retVal = $this->socket_send_str('EHLO '.$hosth, '250')) {
+					$this->_setErr(126, '"'.$hosth.'" does not support authenticated connections. Error after sending EHLO '.$hosth);
 					return $_retVal;
 				}
 			}
@@ -560,7 +599,7 @@ class SMTPs
 				$this->_setErr(130, 'Invalid Authentication Credentials.');
 			}
 		} else {
-			$this->_setErr(126, '"'.$host.'" does not support authenticated connections.');
+			$this->_setErr(126, '"'.$host.'" does not support authenticated connections. Error after sending EHLO '.$hosth);
 		}
 
 		return $_retVal;
@@ -603,11 +642,17 @@ class SMTPs
 				$hosth = $host;
 
 				if (!empty($conf->global->MAIL_SMTP_USE_FROM_FOR_HELO)) {
-					// If the from to is 'aaa <bbb@ccc.com>', we will keep 'ccc.com'
-					$hosth = $this->getFrom('addr');
-					$hosth = preg_replace('/^.*</', '', $hosth);
-					$hosth = preg_replace('/>.*$/', '', $hosth);
-					$hosth = preg_replace('/.*@/', '', $hosth);
+					if (!is_numeric($conf->global->MAIL_SMTP_USE_FROM_FOR_HELO)) {
+						// If value of MAIL_SMTP_USE_FROM_FOR_HELO is a string, we use it as domain name
+						$hosth = $conf->global->MAIL_SMTP_USE_FROM_FOR_HELO;
+					} else {
+						// If value of MAIL_SMTP_USE_FROM_FOR_HELO is 1, we use the domain in the from.
+						// If the from to is 'aaa <bbb@ccc.com>', we will keep 'ccc.com'
+						$hosth = $this->getFrom('addr');
+						$hosth = preg_replace('/^.*</', '', $hosth);
+						$hosth = preg_replace('/>.*$/', '', $hosth);
+						$hosth = preg_replace('/.*@/', '', $hosth);
+					}
 				}
 
 				$_retVal = $this->socket_send_str('HELO '.$hosth, '250');