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.

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 foo@bar.com is bar.com.
2. A DNS query is used to find the mail server for the domain.  For example, the mail server for bar.com might be mail.bar.com.
3. A second DNS query is used to find the IP address of the mail server.  For example, the IP address for mail.bar.com might be 11.22.33.44.
4. Finally, the email program connects to that IP address on Port 25 and delivers the email.

• 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, including AOL, may refuse email that originates from a residential gateway.  Unfortunately, there is no work-around for this.  The only way to determine if this is a problem is through experimentation.
• Some domains claim that they do not accept emails from dynamic IP addresses.  This includes AOL, AT&T, Juno, Mindspring, and Netzero.  Basically what happens is when connecting to a mail server, it will perform a reverse-DNS lookup on your IP address.  If DNS returns an appropriate PTR record, then you are allowed to send email.  Most ISP's will assign a PTR record to their users, however some do not.  Try sending a test message to one of these domains.  If it arrives, then there should be no problems using Direct Delivery.  In Gammadyne Mailer, you can use the "Check PTR Record" option on the Tools menu to determine if you have a PTR record.
• 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" branch.

Because of these disadvantages, Gammadyne strongly recommends against using Direct Delivery.  The most reliable way to send email is through an intermediate web server with a static IP address.  Even so, 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!