I can’t send mail from my i cloud address though I m getting no delivery failure message

I have realised that emails are not being received from my iCloud and BT addresses when sent on my iPad or phone, but can be sent from my HP laptop (BT Mail only on that machine) Ive done all the usual switch on off things and seem to be able to receive mail and the internet /wifi seems to be working ok. Any body know how to resolve this - please note that I’m barely computer literate so no jargon pleeeeese