How to write SMTP mail servers
Many times, I don't think why I can't send the letter to the other party (POP or IMAP) server, why do you have to transfer it once through a inexplicable SMTP mail server, it is really uncomfortable. If you use UNIX, this problem is very well resolved. You can complete the delivery task with Sendmail, but under Windows? Similarly, there must be some way to open SMTP Server directly to the other party's remote post office server, it is rare to live, is it rare to live? Analysis related protocols (RFC2645, RFC821, RFC1846, RFC1939, RFC1725, RFC1730-RFC1733 ETC.), we will know that direct delivery is actually quite simple. First let's take a look at the delivery process of email: email (Encode) -> a SMTP Relay Server -> Remote SMTP Server (Remote Post Office). Very simple, mail encoding is delivered to an SMTP transfer server, the server is sent back to the letter submission (to the same post office), and is sent to the remote post office's SMTP server according to the priority and the order of the letters. . In other words, as long as we know how the SMTP translation server determines the address of the remote post office SMTP server, you can easily deliver SMTP Relay Server directly to the remote post office server. How does SMTP Relay Server determine the address of the remote post office server? If you are familiar with the domain name resolution, we know what is going on. We know that the address of the email makes a postbox@address.com, mailbox (POSTBOX) and address (address.com), send instruction query to domain name server "Address .com "Remote Post Office server's address to find the IP address of the remote post office SMTP server, the instruction query is the address query called the MX (Mail Exchange) mail swap server. The address of the remote post office SMTP server may be more than one, at this time, you can send the corresponding priority letter to the corresponding address of the remote post office SMTP server according to the differential priority, of course, you can also do no matter how Just choose an SMTP server to send, see the "domain name analysis result sample". Simple. This is not difficult to write a SMTP server! Question: The head id is a trouble, sometimes generating an incorrect of Invalid Head ID 5811.
