550 Access denied - Invalid HELO name


I have a user complaining about not being able to send emails using Windows Live Mail. She claims that everything was working fine and the problem started suddenly, without having made any changes. She’s in a different city from me, so I can’t go take a look.

The error message says:

The message couldn’t be sent because the server has rejected the sender’s email address. The sender’s email address was [her correct address].

Server error: 550
Server reply: 550.Access denied - Invalid HELO name (See RFC2821
Server: friday.mxlogin.com

I translated the first part because she has the mail client in Spanish, so it’s likely not verbatim to what Windows Live Mail says in English.

I googled “invalid HELO name” and most articles said that the most likely error is failure to set up authentication on the client for the outgoing server. That wouldn’t start out of nowhere, but anyway, I sent instructions on how to configure the authentication. She says that the error remains, and that she even had someone more knowledgeable than her to take a look.

All other email accounts are working fine and I don’t have her account restricted or anything, so I’d bet this is a client error, but is there anything that could be causing this server-side? Or do you have any tips on what to do?


This means that their email client isn’t trying to authenticate through us. Rather, it’s trying to send mail TO us as if it is it’s own mail server. Anyone connecting to our servers without authentication is considered an external sender and subject to proper standards for running their own mail server.

If their email client is configured to authenticate on SMTP, it would be safe to say that the email client is experiencing a bug.

I bet she did change something and now there’s something wrong with the client’s configuration, but it’s hard to diagnose the problem at a distance and when the other person has a very basic knowledge of computers.

I gave her instructions on how to use the webmail. That’ll have to do, for now.

Thanks again!