who can help me to solve that problem... When I finished to install MailServer on CentOS 5 using Qmailtoaster but I can't send mail. That alway measage to me error: "Server replied: 511 sorry, can't find a valid MX for sender domain (#5.1.1 - chkuser)"... I don't know how to solve that problem so need to help of everybody...
Best regard!!!

Hi,

You are lucky somebody takes the time to answer your question ... HELP ME!!! is not really what I call an appealing subject, I usually stay clear of them. But I know SMTP can be hard, so I feel pitty, which is not really a good start.

Anyway, your error message says it all:

You do not have an MX record for your domain. That means you have a domain, but you need to set up an MX (Mail eXchanger) DNS record for your domain. so, you should go to your registrar's website and add an MX record there for your domain, point it to the IP Address of your SMTP server. Then see what the other server says ...

I agree with thecarpy. You can temporary check whether your mail server is working by using ipaddress directly in outlook/evolution/thunderbird in place of domain/mail server name or edit hosts file to point to the mail server ip address.

We know his SMTP server is working, because the recipients mail server is receiving the email and checking if the the From address is valid, to avoid SPAM. So the mail server attempts to check if his SMTP server knows of a user with your email address, if this fails, the email is dropped - SPAM is suspected. Here, the recipients mail server is looking up his domain, asking for the IP Address of his mail server (MX record), however, the DNS server for his domain sends back nothing or an illegal reply. I guess he does not have an MX record for this domain, or the IP address it contains is wrong. Please check the MX record!

This is a message from the recipients mail server:
"Server replied: 511 sorry, can't find a valid MX for sender domain (#5.1.1 - chkuser)".

For your problem

FIrst configure your DNS record

First a MX Record
Second an A record
Third Most important one creat a PTR record

You can ask your ISP to the above

The above 3 will solve your problem permanenttly

Good Luck

Thanks for your answer... but I don't know how to do that.. I'm a beginer, i only want to create a MailServer to test in LAN..Could you guide to me details? Thanks

Hi

As a beginner you can use the article on linuxhomenetworking.com
It covers on sendmail and DNS related configuration

Good Luck