Gammadyne Corporation

Direct Delivery

The term "Direct Delivery" describes the ability of an email program to deliver email directly to the recipient's mail server, without relaying through an intermediate mail server.  This feature has nothing to do with spam - all email is sent with Direct Delivery at one stage or another.  All mail servers use Direct Delivery except for email that is addressed locally.

How It Works
Following is a step-by-step procedure that an email program uses to perform Direct Delivery.

  1. First, the domain name is extracted from the email address.  This is the portion of the email address that follows the '@' sign.  For example, the domain name in is
  2. A DNS query is used to find the mail server for the domain.  For example, the mail server for might be
  3. A second DNS query is used to find the IP address of the mail server.  For example, the IP address for might be
  4. Finally, the email program connects to that IP address on Port 25 and delivers the email (using the SMTP protocol).

  • Because Direct Delivery is not relayed, this eliminates a point of failure.
  • Reduces the danger of an ISP revoking an account due to sending excessive email.
  • There will be fewer bounce-backs because the email program will know immediately whether or not a message could be delivered.  Unfortunately, many mail servers will accept the email, even knowing that the recipient does not exist, and later send a bounce-back.
  • No Relaying Denied error messages.

  • Some domains require a "Reverse-DNS" record (also known as a PTR record) for the sender's IP address.  Most ISP's will assign a PTR record to their users, however some do not.
  • Some domains will refuse email from any IP address that is on the Policy Block List (PBL).  This includes most IP's that are assigned dynamically or behind a residential gateway.  This makes it impossible to send directly from dial-up, cable, and ISDN connections.
  • Direct Delivery is slower because two extra DNS lookups are required, and because it takes longer to connect to 5 different servers than it takes to connect to one server 5 times.  However, an email program that is multi-tasking can largely eliminate this disadvantage.  Multi-tasking is the ability to send multiple emails simultaneously.  Even when one task is busy waiting for a DNS query, another task can be making progress sending an email.  Gammadyne Mailer can send up to 1024 emails simultaneously.
  • Some mail servers employ an anti-spam technique called Greylisting.  The server will reject incoming emails until a certain time period has elapsed, usually an hour.  Hence, a Direct Delivery mailer needs to keep retrying the delivery for up to four hours.  To accomplish this with Gammadyne Mailer, check the "Delayed Retry" box on the "Send/Delivery" branch.

In Gammadyne Mailer, use the "Direct Delivery Possible?" tool on the "Test" menu to determine if your computer's IP address has a Reverse-DNS record and is banned by the Policy Block List.

Because of these disadvantages, Gammadyne recommends against using Direct Delivery.  The most reliable way to send email is through an intermediate web server with a static IP address.  The server is usually one of the following:

  • Your business's web server.  This will achieve the highest success rate at no additional cost.
  • Your ISP's mail server.  They will almost certainly limit the amount of email that they are willing to relay for you.  And there is an increased chance of your email being considered spam.  Furthermore, you risk being dropped as a customer if they believe you are spamming.
  • A free email service like Gmail.  However, be aware that the number of emails will be severely limited (100/day for Gmail).  And if there is a high number of undeliverables, they may cancel your account.
  • A paid email service such as Google Workspace.
  • An SMTP relay service.  We recommend, TurboSMTP, and  This is still vastly cheaper than using an email service.

Whatever you choose, it is important to keep your mailing list clean of bad addresses.  Attempting to send a lot of undeliverables will incur righteous wrath from the big domains.  And of course, don't spam!