Emails to own domain name bouncing back

[#1]

Hi, we have the mcs.net.uk domain associated with our Plusnet account but emails are not getting through to us. Senders to the domain get:
avasin11.plus.net gave this error:
Invalid Recipient <email address>
A problem occurred during the delivery of this message to this e-mail address. Try sending this message again. If the problem continues, please contact your helpdesk.
We know these emails were working yesterday but this has been going on for about 4 hours now.
The email addresses are still showing in our account and still work if you change the mcs.uk.net domain name to our Plusnet details.
Plusnet, what's not working?!

[#2]

I assume the domain name typed on the first line (order of levels) is a typo? Must be since the message wouldn't even get to Plusnet if that was wrong.
It looks like the mail server has lost the mapping for your domain. Plusnet would have to fix that.

[#3]

Quote from: MCSWilliams

avasin11.plus.net gave this error: Invalid Recipient <email address> A problem occurred during the delivery of this message to this e-mail address. Try sending this message again. If the problem continues, please contact your helpdesk.

Are you still having problems with this?
I've just tried sending a message to the domain and it seems fine?

220 avasin09.plus.net Plusnet Cloudmark Gateway ESMTP server ready
ehlo cm
250-avasin09.plus.net hello [84.93.219.165], pleased to meet you
250-SIZE 104857600
250-8BITMIME
250 OK
mail from:<me@privacy.net>
250 <me@privacy.net> sender ok
rcpt to:<********@mcs.uk.net>
250 <********@mcs.uk.net> recipient ok
data
354 enter mail, end with "." on a line by itself
subject:test from support, please ignore
this is a test
.
250 LDc91l0043aiV8c01DcLTM mail accepted for delivery

I'm guessing you've since managed to sort the problem out?

[#4]

Hi guys, many thanks for your responses. We are now receiving emails fine again.
The problem we now have is we want to add the mcs.uk.net domain name in to Office365 which requires the addition of a TXT or MX record to confirm ownership. As Plusnet don't allow the addition of txt records, I tried before the weekend to add the MX record but this still isn't showing up (Is it becuase we are having our emails delivered to Plusnet's POP3 servers?). The instructions we have are to add either:
TXT @ or mcs.uk.net MS=ms97623250     1 Hour
MX  @ or mcs.uk.net ms97623250.msv1.invalid.outlook.com 1 Hour
Why does Plusnet have such a poor DNS management system for one and second, has anyone managed to get Office365 working with a Plusnet domain? Is it possible a Plusnet employee could add the TXT record required?
Many thanks

[#5]

Quote from: MCSWilliams

Is it possible a Plusnet employee could add the TXT record required?

No, our domain control system doesn't support the addition of TXT records.
You'll need add the custom MX record and move away from POP3 by selecting the option shown in the attached screengrab.