A mail server will produce a "Relaying Denied" error when an unauthorized user attempts to send non-local email through the server.  Non-local email is email which is addressed to a different server.

Mail servers will not relay mail from just anyone.  Otherwise, spammers could flood the mail server, making it do their dirty work.  You must be authorized to use a mail server.  Unauthorized users will always receive the "Relaying Denied" error.

Note:  this error has nothing to do with the software that actually sends the email.

To use a mail server, you must prove to the mail server that you are authorized to send email.

• The sender of the email must be a user on the server.  In Gammadyne Mailer, this corresponds to the "Sender:" field on the "Headers" branch.
• The "From:" email header should be a user on the server.
• If the mail server is on a Local Area Network, it may be necessary to specify the mail server's local IP address, not its name.
• This error can sometimes be circumvented by first checking for incoming email.  Some servers are smart enough to recognize that when you are properly authenticated to receive mail, then you should also be able to send mail.
• It is also possible that the mail server will only relay mail for users that are currently connected to the ISP.  If you want to be able to send mail when using a different connection, you will need to ask your ISP if "SMTP authenticated login" is supported.  If it is, they will give you a user name and password.
• Occasionally, a mail server may require that the email program say hello properly.  This corresponds to the HELO or EHLO command in the SMTP protocol.  The mail server may require that this command reports a proper domain name that is authorized to send email.  Even though this practice is discouraged, some mail servers perform this check as a form of spam prevention.  In Gammadyne Mailer, this corresponds to the "Override EHLO Domain" field on the Send/Details branch.

The only other solution is to not use the mail server at all.  When using Gammadyne Mailer, you can check the "Direct Delivery" box on the Send branch.  This will bypass the SMTP server altogether, and deliver each email directly to the recipient.  This has the additional benefit of eliminating a point of failure.  However, please read the entire article on Direct Delivery so that you understand the disadvantages.