Thanks again folks, the problem has gone on for the last two weeks, tried re-booting my Apple Mac but didn't expect it to resolve the problem as it happens across all three platforms that I use, incl my Samsung S3 phone & S10 tablet. It seems that btinternet accounts reject all my emails as well as some more obscure ones but by no means all so am having to ask friends & family to forward my emails on. Very frustrating!
R2