Provider is Virgin media (blueyonder.co.uk) - Yes, can access mail through their webmail OK.
But mail on Mac will not access - just gives message "Blueyonder IMAP server - imap4.blueyonder.co.uk rejected password for user gill.lloyd108". Up to yesterday all was well so no idea why this happened, etc.......
This is going back a while but I remember there were specific settings for email to work on iPhone/iPad etc, so this may help as I used to be with Virgin Media.
It looks like you are using IMAP from what you've said, so make sure you follow the details under the IMAP heading.