So for a while now I was getting a lot of messages that were absolutely fine on my phone BT email client but on Outlook on my PC, showed with unknown sender and no subject.
I read all the previous stuff about only affecting POP3, wasn't that since I'm using IMAP but then I realsied I had Outlook configured against both my @talk21.com address and the associated [email protected] address.
I removed the .t21 address from my outlook settings and 'boom' all the emails it couldn't read in my inbox instantly corrected.
Hope this maybe helps someone else configured the way I was.
