Question on Email transiting rules

I haven't poured over the RFCs on this one and was hoping that someone would know off-hand.

Pretend I have a basic mail server example.com

I telnet into example.com at port 25 and do something like this:

EHLO hi
MAIL from: me@example.com
RCPT to: meagain@anotherserver.com
DATA
Hello world
.

I think that is valid syntax (if not, let's pretend). I know email can get rather complex, so I'm trying to avoid the nuances.

Now would I be correct in the following assertion:

1. example.com finds the MX record for anotherserver.com, assume m开发者_C百科ail.anotherserver.com
2. example.com does a DNS lookup of mail.anotherserver.com, assume it's 1.2.3.4.
3. example.com routes the message directly to 1.2.3.4 without any mail-specific relay interlinks.

In other words, with DNS lookups, there is a DNS-level hierarchy and when you lookup a DNS record, you hit many machines, some of which you probably do not own and may have some 'abuse detection software' on it.

The Question:

Is email the same way?

• Would there be hierarchical next-level e-mail level routing authorities between example.com and mail.anotherserver.com?
• And if so, would they possibly add my servers to blacklists simply because they are transiting large volumes of mail between each other?
• If this is so, how would one do extensive testing of email-based services?

I know the answers to these questions circa about 2004 or so. I also know that email gets lots of strange rules applied to it; and haven't been keeping up with all the technology surrounding it. I don't know if any exceptions to the old rules have been deployed en masse recently.

Any insight into the transiting rules would be much appreciated. Thanks.

Your SMTP server (I assume you are using SMTP) will simply make a TCP connection to the remote SMTP server once it has resolved the DNS address. Once the connection is made it will transmit the message.

However, during the transmission you will be sending information across the internet which means the information will likely go to your ISP and then through a backbone to the destination ISP as part of the normal routing process. There is no additional routing or communication with external machines as part of SMTP.

Any of these middle services (most likely your ISP or their ISP) may complain about excessive data transfers if it violates any contract you may have.

Also, the destination SMTP server could very well blacklist you if they don't appreciate the large volume of mail.

However, if you owned both SMTP servers and had a normal contract with your ISP you shouldn't be blacklisted for this as you won't be accessing any other servers as part of the SMTP process.