550 Invalid Recipient ?

[#1]

Just started to use my plusnet email. I can send messages but  all messages sent to it are rejected with this message
Delivery to the following recipient failed permanently:
username@username.plus.com
Technical details of permanent failure:
Google tried to deliver your message, but it was rejected by the server for the recipient domain bumbershoot.plus.com by mx.avasin.plus.net. [212.159.9.200].
The error that the other server returned was:
550 Invalid Recipient username@username.plus.com
Whats wrong?
jim:green actual email address munged to avoid spammers mod:end

[#2]

First thing is to look here and see if the email on your account is active
https://portal.plus.net/my.html?action=myemail&s=1&redirected=yes&?membermenu=emailsettings and click on manage my mail

[#3]

Fixed it. Address should be,  myname@username not username@username.  No idea why it was like this. I didn't choose it.

[#4]

Apparently, you can have as many email addresses as you like, so if you want to use username@username, you can add it in the Member Centre.