Hi to all" I have a VPS for email sending.All is ok,but it is not possible to send email to GMAIl. Only to GMAIL. The return is: host [18.104.22.168] SMTP error from remote mail server after pipelined end of data: 550-5.7.1 This message does not have authentication information or fails to pass 550-5.7.1 authentication checks. To best protect our users from spam, the 550-5.7.1 message has been blocked. Please visit 550-5.7.1 for more 550 5.7.1 information. l17si5709570wmj.118 - gsmtp Any ideas why? Thank you very much!