iPhone Mail app can't receive email (IMAP AUTHENTICATIONFAILED) for two days — sending still works

Since Sunday evening, my husband's Xfinity email has stopped receiving on his iPhone (Mail app), while sending still works fine, and everything works normally on his laptop via the Xfinity webmail.

On the iPhone, he gets this repeating error:

"Password incorrect. Enter password for IMAP." — Comcast

(Normally the email app on his phone would not require a password.) After he enters the correct password for his email, it then shows:

"Cannot get mail. The mail server 'IMAP.comcast.net' is not responding. Verify that you have entered the correct account info in Mail settings.
Server code: AUTHENTICATIONFAILED
Server message: authentication failed"

(He is offered the choice of "Cancel" or "ok.")

Details:

• Webmail on a laptop works perfectly — new mail is arriving normally
• Sending from the iPhone Mail app still works
• Only IMAP (receiving) on the iPhone is affected
• Third Party Access Security is enabled in account settings
• No security alerts shown on the account
• Restarting the phone, toggling Airplane Mode, and toggling the Mail account off/on did not help

Can Comcast/Xfinity help? Would prefer not to reset the password if this is a server-side glitch. Thanks.

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