Plusnet rejecting mail for registered domains

[#1]

I normally have mail delivered by SMTP but I'm having mail server issues (at my end) which will take some time to fix  so as a temporary measure I have switched my plusnet email and my two registered domains to POP3/IMAP delivery. I can see that the MX records have been updated ( apparently correctly) and email to <users>@<myusername>.plus.com are being accepted and delivered correctly.
But all emails to my two registered domains are being rejected by Plusnet's mx server, with permanent errors due to ' invalid username'. As a result I'm losing email. I've tried switching spam filtering on and off, which changes the MX record but still results in rejection of all email.
I've opened a support ticket but after more than 48 hours I'm yet to get even a response from Plusnet support. Not impressed.
Any suggestions? Please help.
Thanks,
Paul

[#2]

Hi Paul
Welcome to the forums, I have sent a PM to someone who should be able to help you, but you may need to wait until monday for some help, I am sorry but most of PlusNet's staff don't work on a weekend any more, once over they did do!

[#3]

It seems they don't work Fridays either.
But thank you for your effort. Much appreciated.

[#4]

Apologies for the delay Paul, I've just bounced your support ticket back to you. Unfortunately it's a tad difficult for me to ascertain what happened here now that your domain is pointing to your SMTP/backup server again

[#5]

Quote from: paulburnsuk

But all emails to my two registered domains are being rejected by Plusnet's mx server, with permanent errors due to ' invalid username'. As a result I'm losing email. I've tried switching spam filtering on and off, which changes the MX record but still results in rejection of all email.

Have you setup the domains in your PN control panel or asked PN to accept mail for them? - You can't just point domains MX records at a mail server that has not been configured to accept mail for them. The mail server must be setup to handle those domains or it will reject mail addressed to them.

[#6]

Hi 7up,
  Thanks for the reply. I was using Plusnet's  portal control panel to switch my domain's email delivery options from IMAP/POP3 to 'SMTP to my static IP'.  That triggered the DNS updates, and should also have updated plusnet databases to allow email for my domains to be accepted. The response I eventually received to my support ticket suggested that the database update probably didn't happen for some unknown reason.
Unfortunately, it took so long to get any response I was forced to subscribe to a 3rd party backup MX service to prevent losing all my emails. So, as you'll see from the Plusnet response above, we'll probably never know exactly why it went wrong.
Cheers,
Paul