Had this issue on my laptop. Came home, launched Outlook 2010 and did a send /receive and got the error seen below.
On my local setup I had changed NOTHING, I mailed my web-host and again nothing had changed, passwords where ok etc.
Now, what had changed is the week before I had moved ISP`s from BT to SKY. It seem like SKY wanted to authenticate to be able to send mail out ( I could receive mail fine ). Follow these steps to fix the The Server Responded 550 Access Denied – Invalid HELO Name See RFC 2821 18.104.22.168 error.
Go to your mail account properties then select “more settings”.
Once you are there. Select the Outgoing Mail tab. Put a tick in the option for “My outgoing server (SMTP) requires authentication. Also use the same settings as you would for receiving email
Once done select ok. Try to send and receive, you will now find that you do not get the 550 error in your outlook client.
Tags: RFC error