How do I stop duplicate emails from Plusnet

[#1]

Hi,
Just moved to Plusnet and am getting every message from them in duplicate, is there any way to cut it down to one of each message?
I found something in an internet search that said to set-up a 'postmaster' mailbox but it hasn't helped, unless I haven't done it properly.

[#2]

Hi there,
I've had a quick look at your account and can suggest a change to your mailbox settings with us which should fix this.
I'd delete the mail alias you've already got set up and create a new mailbox right <a href="https://portal.plus.net/my.html?P%2BVHYN6YBvn5XnJBpBx5LxGvNgoXUgKqC3f0fFmIgOsmrrsujjYNOoAbUr2%2FgAxC&redirected=yes">here</a>
Following that you'll just need to make a quick change to how the username is configured by following this format username+mailbox name (don't bother including the .plus.com bit in the username).
That should resolve that for you.

[#3]

Thanks for the quick reply.
If I click on the link you gave I get "Unfortunately, this feature is not available with your current account." and other stuff.
Can I do it through 'member centre' - 'manage mail', and I'm not really following the bit about username config, is that on the new mailbox and should it be entered exactly as "username+mailbox" or usernamemailbox, username@mailbox ?

[#4]

@Adam,
Just what was that link?  It fails for me too and my account is quite old!

@Fockewulf,
Try this - https://portal.plus.net/my.html?zYc5AJRX0KbfbnbZc6p4ORGvNgoXUgKqC3f0fFmIgOsmrrsujjYNOpU3WeE3zzzA0Nur... - instead.
Adam's description is clear if you know what you are doing. 
If you create a new email box called fred@username.plus.com when you configure your email program to access it, the username you need to specify is username+fred with the same password you used when you created fred.

[#5]

Townman, I'm afraid I am still getting the same page with "Unfortunately, this feature is not available with your current account." etc., from the link you gave.
I use Thunderbird for email and it doesn't seem to like me adding '+mailbox name' to the username, the mailbox name has an '@' symbol on the end - should I add that as well.
I did notice that after I deleted the postmaster alias from my account I only received one confirmation email and I have only had one email notification of topic reply.

[#6]

Maybe a simpler fix is to look here - https://portal.plus.net/my.html?action=edit_details&s=0 - and ensure that your contact address is postmaster@accountname.plus.net
Not sure how you have deleted the postmaster address - AFAIK it MUST exist as either a mailbox or an alias on the default mail box.
PlusNet send all communications to (if they are different) both the contact email address and postmaster@

[#7]

Thanks, have put the alias back so will see how it goes, there was a dustbin symbol next to the postmaster alias and I just clicked on that to delete it. I wasn't getting anything incoming with putting  'username+mailbox name' in thunderbirds server settings.