How do I send mail directly to a recipient's mail server?

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To send mail directly to another SMTP server, you do the following:

 

1.Do a MX (Mail eXchange) DNS lookup on the domain name. 
2.Connect to the machine address returned by the MX records you consulted.
3.Submit the E-Mail using the SMTP protocol.

 

In Indy 8 and 9, the SMTPRelay Indy demo illustrates how to do this using Indy.

 

In Indy 10, you may wish to use the TIdSMTPRelay component.

 

Some people will have problems with sending mail directly to a recipient's mail server and thus, would have to use their ISP's mail server.  Those problems are:

 

Some Internet Service Providers firewall users at port 25 to make it impossible to send E-Mail directly to a recipient's server.  This is a security measure that Internet Service Providers take so users can not bypass SMTP server logging that Internet Service Providers uses to trace users that spam.
The IP address being used by a PPP dial-up user may be blacklisted.  This means that the a SMTP server using the blacklist may refuse to accept E-Mail from that machine.
Many Internet users do not know the address of their DNS server.  Often, this information is provided by the Internet Service Provider when the user logs into their PPP dial-up account.  Some ISP's also provide users with some type of automated setup utility that automatically configures the appropriate settings without the user knowing what the settings are.