random emails from last year being delivered to my outlook express email inbox

[#1]

I have a plusnet account but a madasafish email address which I kept when I changed providers.  Why do my old emails (from as long ago as 7 months ago) keep coming into my inbox?  Also why are new emails sometimes being tagged onto the bottom of these old emails, along with lots of codes.  I have three madasafish emails addresses and my husband has one.  Sometimes my emails go into his inbox and his into mine.  I have filters set so that the correct addresses go into the correct boxes.  All this is driving me mad.  I did contact both Madasafish and Plusnet last year and it did seem to improve but now it's back again.

[#2]

It would help to know what you're using to access your mailboxes and how. i.e. IMAP or POP3? Are you leaving a copy of the messages on the server? What happens if you log into Webmail, does everything look OK there?
It sounds to me like you might be accessing your email using POP3 and leaving a copy of the message on the server? If that's the case, then the symptoms you describe can sometimes be attributed to problems with the UIDL history of the email application you're using. There's an example of the sort of thing I'm talking about here (although it's not Plusnet-specific).