Confirmation of mail collection

[#1]

Hi all,
Recently had a few problems with the pc which I think have now been rectified other than the following -
My situation now, is that I do not know if my email client (Windows Mail Vista Home Edition) is collecting all emails from the 3 plusnet mail boxes we have.
Mine is working ok and I have been trying to get people to cc test sends to the other two but nothing has arrived since Thursday evening.
I set up one for my wife a few years ago and it has worked fine up to Thursday night, but now we are not receiving emails from her mailbox address, so I set up another mailbox for her and we are not getting emails from that one either.
Is there any way of checking that there isn't a backlog of emails?
Any assistance would be much appreciated.

[#2]

You can use Plusnet webmail (https://webmail.plus.net) to check for emails in a particular mailbox. Remember that for the default mailbox you need to login using just the account username and the account password. For additional mailboxes you login using username+mailboxname and the mailbox password. This applies whether using webmail or an email client on your PC.
If you use webmail to send messages, you need to make sure the sender identity (reply address) is set correctly (in personal settings), ie mailboxname@username.plus.com . For testing  purposes you can send messages from one mailbox to another without needing third-party help.

[#3]

Thanks for the info. I am not quite sure if I have interpreted your instructions correctly.
I have logged into plusnet webmail but cannot 'see' any of my other mail boxes. What am I doing incorrectly?
I thought that once inside webmail, that I'd be able to see the other mail boxes and then log into each one.
OR - Do I log out of webmail and log back into it using a different log-in?
Apologies for highlighting my obtuseness but I have never used the webmail facility before.
EDIT: I have managed to sort it - many thanks.