Hello,

I've installed a smtp server in a machine and I'm trying to send messages to differents recipients. The problem is that there is a domain where they are rejected by their firewall and I don't know the reason.

The configuration of my network is as follows:

I have a ADSL solution, whith a ADSL router with many PCs connected. This PCs has a private network configuration (192.168.0.*), and one of them has a mail server installed.

I've talked to my domain provider and I've asked him to put an MX record in the DNS.

I received mail whith my mail server.
I send mails to other mail addresses.
But there is a domain which doesn't accept my messages. I've used a packet analyzer and it seems that the packet are stopped in a router/firewall.

Which could be the problem? How could I resolve it?

Thank you.

Hello

You could try telneting to your SMTP server on port 25 and transferring an email using the command line.

The email program you use does this but hides it from you so you dont see what goes on in the backround except when you get those errors or failed messages.

The commands you would use to talk to the other domain should be in the sniffer trace you took,
You could issue those commands , see which one fails and then it should hopefully show you where the problem is.

A sample of a transaction should look like this

telnet `smtp.com 25
smtpserver ready

HELO remotedomain.com
hello pleased to meet you
MAIL FROM: me@here.com
ok
RCPT TO: You@there.com
recipients ok enter

etc.
most should respond to this.
Give it a try see what happens

Cheers