• Smart host service is an optional service that may be made available to qualified^* clients on a case by case basis.
• Authentication is required in most cases and especially after a service suspension.
• IP based access requires verification that the authorized IP address is not shared with multiple hosts. Specifically, the outgoing public IP address of your e-mail server must be configured such that no other hosts are using that IP address.
• Envelope sender addresses that don't match the list of allowed sender domains are not accepted.
• We strongly recommend that you follow our recommended incoming SMTP configuration to help prevent these types of problems.  By only allowing access from the predefined list of ETRN.com IP addresses, you prevent other hosts from directly  accessing your server.
• We strongly recommend that you follow our recommendations below, as doing so will greatly reduce your risk of ending up being listed by a DNSBL:
  1. Securing NAT
  2. How To Avoid DNSBL Listings
• "Bounce" e-mails (e-mails with a null "<>" sender address) will not be accepted from hosts that do not have a recipient filtering method defined. Please see: Recipient filtering methods compared for a comparison of the available recipient filtering methods.
• Limits (if you need higher limits, please contact us to discuss your options):
  • Maximum recipients per e-mail: 100
  • Maximum concurrent connections: 50
  • Maximum connections per minute: 50
  • Maximum e-mails per minute: 120

* To be a qualified client, you must meet at least the following qualifications:

• Your server must not be an open relay.  Open relays are also often used by spammers to send their e-mails.  By default, virtually all modern e-mail software is configured to not be an open relay by default.  Misconfiguration and compromises are often the cause of this condition.  See (http://www.google.com/search?q=prevent+open+relay) for information on how to prevent (and correct) this type of problem.
• Your sender domain(s), HELO host name, and your server's DNS PTR record must not be listed on the Spamhaus DBL DNSBL.  E-mail will not be accepted if your sender domain(s), HELO host name, or your server's DNS PTR record are listed on the Spamhaus DBL DNSBL.
• Your server's IP address must not be listed in either the Spamhaus XBL DNSBL, Spamhaus SBL DNSBL, or the spambl.etrn.com DNSBL.  E-mail will not be accepted if your server's IP address is listed in either the Spamhaus XBL DNSBL, Spamhaus SBL DNSBL, or the spambl.etrn.com DNSBL.
• Additional requirement may apply, especially if you have made recent changes to your systems or had a recent compromise of your systems.