I have had the same BT email address since before I worked for BT, many years ago. I can use the online email to send/receive but on iPhone and on outlook I can only receive. It keeps asking for my password. This is quite random, because not long ago I could use both ways - it just stopped working and asking me for a password. I have ticked the box and still no luck.
I used to use Yahoo but was transferred to BT email.
Are BT trying to get rid of free email addresses, even though I worked for BT for ten years.