SMTP authentication is an extension of the ESMTP protocol. It allows the mail server to authenticate clients from their user names and passwords.
My e-mails arrive with a delay? What can I do?
Delays can occur. If an e-mail is delayed, you will receive a warning. If an e-mail does not arrive, you will receive an error message. When e-mails have several recipients, some recipients might receive the e-mails with a delay.