Every time I try to login to my email app I get message "Sorry! Please try again later". I've uninstalled and re-installed the app twice, cleared caches and browsing data and have rebooted the phone, all to no avail. Any suggestions?
can you access your BT mail using a web browser? Have you tried a 3rd party mail app bluemail or Gmail?
Are you presently a BT Broadband customer or are you paying for your email through a BT Premium email account or did you migrate to EE Broadband?
If none of the above your email account may have been downgraded to a BTMail Basic account which can not be used with an email client or email apps.
See link
https://www.bt.com/help/email/bt-email-products
If you are one of the above try installing the BlueMail email app to see if that works.
Migrated to EE broadband ages ago, never had a problem with Email app befgore