The mail user reports the error:

Task user@domain.com – Sending reported error (0x800CCC78): ‘Cannot send the 
message. Verify the email address in your account properties. The server 
responded: 550 Access denied – Invalid HELO name (See RFC2821 4.1.1.1)

Corresponding entry in Exim logs say:

2014-09-24 07:06:31 H=isp-ip-dom.net [xxx.xxx.xxx.xxx] rejected MAIL 
<user@domain.com>: Access denied - Invalid HELO name (See RFC2821 4.1.1.1)

At Bobcares help desk support services, this is a common error we see in DirectAdmin shared hosting servers. Strict anti-spam rules or lack of SMTP authentication usually cause this error.

Given below are a few scenarios we’ve encountered, and the solutions we provided for them.

Disabled SMTP authentication in mail clients

POP-before-SMTP was the first effective method to restrict SMTP server access to only valid users. It though had a few loop holes that allowed un-authorized individuals to send mail. SMTP authentication solved all these problems, and is enabled by default in latest versions of DirectAdmin.

However, many mail clients do not have SMTP authentication enabled by default, and this causes the SMTP communication to break immediately after the initial “HELO” hand-shake. This is the root cause of the “Invalid HELO name” error. In such cases, we explain the need for SMTP authentication and provide detailed steps to the web master to configure their mail client correctly.

Listed below are the steps we use to configure some common mail clients:

Microsoft Outlook

1. From the Menu Bar, Click Tools then Click E-mail Accounts
2. Select "View or change existing e-mail accounts" then Click "Next"
3. Select the Email account and click "Change"
4. Click "More settings"
5. Select the "Outgoing Server" tab
6. Select the box beside "My outgoing server (SMTP) requires authentication"
7. Select "Use same settings as my incoming email server"
8. Click OK, Next and then Finish.

NOTE : In Outlook 2010 and later, the Email account can be selected by going to Menu bar >> File >> Info tab >> Account Settings

Windows Mail

1. Go to Tools > Accounts. 
2. Select the "Mail" tab. 
3. Select the mail account and click "Properties." 
4. Go to the "Servers" tab, and check "My server requires authentication" under Outgoing Mail Server. 
5. Press "Settings," select "Use same settings as my incoming mail server," then press "OK" on the next two screens to save the changes, then press "Close".
6. Finally, restart Windows Mail.

Thunderbird

1. From the Menu Bar click Tools, then Account Settings
2. This will bring up the Account Settings window where you can click on Outgoing Server (SMTP) at the bottom of the list in on the left side of the window.
3. Select the appropriate outgoing server and click on Edit.
4. Make sure "Authentication method" is set to "Normal password"
5. Click OK to close the SMTP edit window and again on the Account Settings window.

Mac Mail

1. Within your application click Mail, Preferences, and then Accounts
2. Where it says Outgoing Mail Server (SMTP), click the drop down arrow and select "Edit SMTP Server List..."
3. Click the Advanced button and make sure Authentication is set to "Password."
4. Click OK to close the edit window

Improper SMTP authentication in PHP/Perl scripts

Most of the web applications have the capability to send mails. While the majority of them use /usr/sbin/sendmail to send mails, some can be configured to relay mails through an SMTP connection to the mail server. Some web masters and developers miss out giving SMTP authentication information in the web application, leading to errors like below:

Warning: mail() [function.mail]: SMTP server response: 550 Access denied - Invalid HELO name (See RFC2821 4.1.1.1)

In such situations we help the web master in the troubleshooting which variables need to be edited to enable SMTP authentication.

Enforcement of strict RFC compliant HELO

In an effort to combat spam, some web hosts enable strict checking of HELO. This causes some web application hosted on a inadequately configured dedicated IP to be denied mail relay access. In such cases, we help the web master get a fully RFC compliant IP and host name.
A variety of factors can lead to an error. At Bobcares help desk support services, we rely on systematic troubleshooting, that enables us to quickly and accurately resolve any email issue reported by customers.

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