ESN . POSTMASTER

Extra Security Networks


Email Acceptance Policy

ESN is committed to the goal of elimination of unsolicted email. As a result, ESN maintains a very strict anti spam policy.

Strict RFC Compliance
We will reject email that is sent from servers that are not configured correctly. We will not whitelist or make exceptions for specific servers that are not configured correctly. It is the responsibility of the administrator of the sending server, to properly configure their mail server.

Proper Configuration of Sending Server

  • The IP address of your mail server must have a reverse DNS record (PTR)
  • TheThe sending server must have proper FcrDNS (see Best Practices)
  • The sending server must have a valid helo/ehlo greeting (see Best Practices)
  • The "from" email address must exist
     
  • FcrDNS testing tool
  • MAAWG documentation regarding FcrDNS (see page 5)


Domain, IP and Network Reputation
We will permanently reject email from domains, IP addresses, and entire networks that have a poor email reputation. Reputation is determined via third party services such as realtime block lists, and through our own observations and experiences regarding specific senders, networks, and abuse patterns.

If you send spam or unsolicited email to mailboxes on our network, your domain and/or IP address will be locally blacklisted. We will block entire networks, when those networks consistently provide new IP space to spammers or allow spammers to constantly rotate IP addresses.

We share our observations, experiences, and data regarding specific senders, networks, and abuse patterns with several third parties. If your domain, IP address, or network is placed in our local blacklist, there is a very good chance that your domain, IP address, or network will shortly appear in a major RBL.

Reputation Resources

  • MX Toolbox provides agregate block list lookups, smtp server diagnostics, and various other tools
  • Spamhaus and Barracuda Networks provide excellent realtime block lists, with very few false positives
  • Web Of Trust provides domain reputation information
  • Senderbase provides domain, IP, and network reputation information
  • Internic provides basic whois information for several TLDs
  • IANA ARIN RIPE APNIC LACNIC and AFRINIC provide information regarding IP network owners


IP Network Location and Age

  • We may run stricter tests on specific IP networks, due to the geographic location of those networks
  • We may run stricter tests on specific IP networks, due to the age of the network assignment
  • Specific mailbox owners may choose to reject mail that originates from specific geographic locations


Email Commandments

  • The sending server must comply with all relevant RFCs
  • The sending server must have a reverse DNS record (PTR)
  • The reverse DNS entry of the sending server, must not be generic
  • The sending server must have proper FcrDNS
  • The sending server must have a valid helo/ehlo greeting
  • The helo/ehlo host name greeting of the sending server must resolve to a public IP address
  • The sending server must not retry delivery after a 5xx error
  • The sending server must not retry delivery for more than two days
  • The sending server must not send to users that do not exist
  • The sending server must not send unsolicited mail to mailboxes on our network
  • The sending server must not attempt to relay third party mail through our servers
  • The IP address of the sending server must be static
  • The IP address of the sending server must not be a dynamic or residential IP address
  • The email must comply with all relevant RFCs
  • The email "from" or "reply to" domain must exist and resolve
  • The email "from" or "reply to" address must exist
  • The email must not contain viruses or links to malicious web sites
  • The email must not contain executable attachments
  • The email must not contain forged, spoofed, inacurate or obscured: headers, content, information, or data
  • Executable attachments are allowed when compressed in a zip or other container file
  • Multiple or large file attachments should be compressed into a zip or other container file