Good to know you can keep in touch using TalkTalk Mail webmail.
Only email accounts accessed by software using insecure encryption would see the message from TalkTalk advising "Our records show that you are still accessing your email using unencrypted email settings, because of this, from 17th February you will no longer be able to receive or send emails via this email app or software".
If the lineone and talktalk email addresses are accessed using the same insecure settings then the talktalk mailbox is likely to have IMAP access removed and be restricted to webmail only access in due course.
The fact that IMAP access is now removed for the lineone mailbox means the email software will not be able to authenticate the password.
What device is running the lineone email software? What's the operating system and email software name and version? Asking because some software will not be using secure encryption to the required TLS 1.2 standard. Or simply that the settings aren't up to scratch.
Are there any other services or devices connecting to the mailbox? Mail collection service, desktop, laptop, notebook, tablet, phone etc. Every one must use secure settings to connect to the mailbox and therefore any one could be the cause of the removal of IMAP access.
