I want to zap my Openworld address

I'm one of the original @btopenworld addresses. I'd like to go over to being @btinternet and I understand that the two are interchangeable. But will my @btopenworld mail still come to @btinternet? The reason I ask is that I tested it from one of my other email accounts and the two messages I sent haven't arrived (after 2 days). I can log into my @btinternet web page OK (so not using OE for this test) and they have definitely not come.

just tried it and sent an email to *******.*******@btopenworld.com and turned up in my *******.******@btinternet.com mailbox straight away