Fix Postfix HELO command rejected need fully-qualified hostname from .NET Client

• 1 You can bypass HELO restrictions for authenticated users by inserting permit_sasl_authenticated before rejecting rules in the smtpd_helo_restrictions list
  
• 2 main.cf:
  smtpd_helo_restrictions =
  # permit_mynetworks,
  permit_sasl_authenticated,<--THIS
  reject_non_fqdn_helo_hostname,
  reject_invalid_helo_hostname,
  ...
  permit
  

References

• https://stackoverflow.com/questions/13062562/net-smtp-mail-error-helo-command-rejected-need-fully-qualified-hostname
• https://unix.stackexchange.com/questions/91749/helo-command-rejected-need-fully-qualified-hostname-error/91753
• https://social.msdn.microsoft.com/Forums/en-US/77f45c5f-76be-400c-a529-a1e49d6d8e62/systemnetmailsmtpclient-fqdn-required?forum=netfxnetcom
• https://www.postfix.org/postconf.5.html#smtpd_helo_restrictions