Suddenly I can't get email on my Macbook or iphone. When I open email on the laptop I get a message stating imap server rejected the password for my email address. On my iPhone the message states the user name or password is incorrect.

Suddenly I can't get email on my Macbook or iphone. When I open email on the laptop I get a message stating imap server rejected the password for my email address. On my iPhone the message states the user name or password is incorrect. Though I've not had to enter the user name or password on either device to access email. I appreciate someone's insight on what's happened and how to correct it. Thank you.