Hi Jon Wilkinson, thanks for raising this. First, the new Outlook app has limited support for legacy account types, especially those configured in Outlook 2010 using POP or custom server settings. Second, if your account is from a third-party provider (e.g, web hosting or private domain), it may not be recognized unless IMAP is enabled. Third, try adding the account manually via Settings > Accounts > Add Account > Advanced setup > Internet email, and enter your IMAP and SMTP details. Fourth, if that doesn’t work, switch to Outlook Classic, which still supports older account types. Fifth, check with your email provider to confirm IMAP and SMTP access is enabled some hosts require manual activation. Lastly, Microsoft has confirmed that the new Outlook is optimized for Microsoft 365, Outlook.com, Gmail, and Yahoo, and may block unsupported configurations. Hope it helps.
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Best,
Carl