Testing HELO configuration
One way of testing whether your mail server is misconfigured is to send an email through it to helocheck@cbl.abuseat.org. You will get a virtually immediate rejection.
In other words, you will get bounce message back that appears to indicate that your email to helocheck didn't work. It did. It's _supposed_ to work that way. The important piece to check is the error message you see.
Examine the error message, and you should see something like one of the following lines:
#5.1.1 SMTP; 550 Your HELO name for IP address 1.2.4.6 was "localhost.localdomain"
#5.1.1 SMTP; 550 Your HELO name for IP address 1.2.4.6 was "localhost"
#5.1.1 SMTP; 550 Your HELO name for IP address 1.2.4.6 was "smtp"
#5.1.1 SMTP; 550 Your HELO name for IP address 1.2.4.6 was "1.2.4.6"
#5.1.1 SMTP; 550 Your HELO name for IP address 1.2.4.6 was "[1.2.4.6]"
#5.1.1 SMTP; 550 Your HELO name for IP address 1.2.4.6 was "mail.example.com"
It should be the fully qualified domain name for your mail server or an IP address enclosed in square brackets.
In the above example, the first four examples are syntactically wrong by RFC2821. The last two are valid.
If it isn't like one of the last two examples, you have found the problem that needs to be fixed.
If the HELO you see from "helocheck" is a fully qualified domain (such as "mail.example.com"), your mail server software is configured correctly, but something else in your environment is attempting to send email, and you need to hunt it down. Check for sender verify code, challenge/response or proxy trojans (common on certain flavours of web servers). Eg: check the running tasks for anything you don't immediately recognize.
Please don't contact us and say "but our mail server software isn't doing it". It may not be, but SOMETHING at the listed IP IS.
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