Hoping someone can help - have I been hacked?!

[WhatsWrongWithYule]

Just tried sending an email to a contact I came across during a web search. Message failed but when I went to my inbox all messages have changed from the dark blue/bold which shows they're unread, to the paler blue of the messages already looked at.
BT call it 'message 553' and seem to want me to change my email address.
Apologies in advance for any stupidity/naivety here - but if I do this, will any new emails automatically be re-directed?

This happened to me last week and I ended up not being able to access e-mails or contacts,I went to yahoo help and posted a question on their help page,it put me back to yahoo mail and told me to choose the old type of yahoo mail not the new page that they are using now,since I have done that all seems ok, and to-day I had a problem with a scam page asking for my BT password and e-mail address i had probs getting the page to accept the password and thank god I did because in the end I telephoned BT and the rep said it was a scam page and he talked me through the procedure to correct things,those BT geeks are fab IMO.Take care until you get it sorted

Oh thanks so much for that - yes the 'error' message inviting me to change my details did come from BT - or said it did.
I haven't done so because it seems a pita to start afresh with a new address - not because i was suspicious.
Will have another look and try and call BT in the morning.