Why my own mail server can not deliver mail to gmail, hotmail etc…?

Question

I am trying to build a mail server using Ubuntu to send mail

I have done some research on that and find it is nearly impossible for a individual to send

the mail eg hotmail , gmail.

The question i am asking is not how to build a own server , it is why i can not build my own server .

To be precise:

Questions:

1) what are the requirements to send to those eg hotmail ,gmail server ? eg mx record , clear dns record . (only from server aspect , not concerning other factors such as headers or mail content), It would be easier to understand if they are listed out.

2) I read some document and it said the problem can be overcome by relayhost, what is it about and is it feasible?

3) For those ISP , what are their procedure in building the mail server? How is it different from my own small Ubuntu one?

Sorry for asking a lot of question, any help would be nice and well appreciated .

Answer 1

Most people use an out-of-the-box package as a mail server, rather than trying to write one that follows all of the relevant RFC specifications for SMTP, Internet Message Format, IMAP4, POP3, etc. I'm not saying "don't write your own", just that if you do, be prepared for months and months of hard work, lots of bugs and even more frustration. It's a big project.

In terms of sending messages, you will need to follow the Simple Mail Transfer Protocol (SMTP) to send messages; and they should be sent to the correct server, as per the recipient's DNS records - see RFC 1034 and RFC 1035 . If you are correctly using SMTP to send valid messages to the right server, there's not a lot else you can do.

Your next problem is going to be reputation. This would be the same, whichever software you use to send your messages. It's easy for a spammer to set up a new mail server and start sending messages, so it will take a while for some mail servers to trust you (particularly those that are regularly targeted, such as Hotmail, Gmail, etc).

Instead of sending messages directly to the recipient's server, you can use SMTP to send the messages to a relay server. This would usually be your own ISP's server, but it can be any willing partner. You would normally need to make advance arrangements, so that they will permit you to relay messages. The relay server would then attempt to send the message to the recipient server. If it cannot do so, it must report the failure to the sender.