As described in this closed topic: Email not working SMTP Relay Gmail
I’ve this same issue e find out the command EHLO is misconfigured sending “EHLO localhost” instead the public IP allowed in my G Suite environment.
For a while, I’ve edited the file [passbolt dir]/vendor/cakephp/src/Mailer/Transport/SmtpTransport;php as follow, just changing the variable {$host} in lines 234 and 238 to the public IP allowed and it works fine. Take in mind that I didn’t change the variable value, I replaced for “EHLO [myIP]”, since this variable is used in other script contexts.
Original
233 try {
234 $this->_smtpSend(“EHLO {$host}”, ‘250’);
235 if ($config[‘tls’]) {
236 $this->_smtpSend(‘STARTTLS’, ‘220’);
237 $this->_socket->enableCrypto(‘tls’);
238 $this->_smtpSend(“EHLO {$host}”, ‘250’);
239 }
Waiting for comments about this workaround, as how to proper set it or if this is a bug in fact.