This one is because you started the hosting with a sub-domain of astahost (or a different domain name) and then you changed it to a new domain name or to a sub-domain name.
If you had setup and was using NeoMail with your old domain / sub-domain name all settings will not be automatically be updated when we change the domain name for you. WebMail have custom settings that you setup first time you use it so the custom setup is what we don't update when we change the domain name for you.
So open up NeoMail and click on the "USER PREFERENCES" setup. The icon looks like an open ended wrench (fix your car not the email) now you are in "USER PREFERENCES" setup and you have to make sure the "From" and "Reply-to" are valid emails.
The issue is that the "From" part of your emails domain name is updated but the "Reply-to" stays the way the old "Reply-to" address was.
This should take care of the 550 issue. This was tested using NeoMail but should be the same for all the web-mail clients in cPanel.
Nils
