Can't add IMAP email account to new Outlook

Question

I am experiencing what appears to be a previously reported issue with New Outlook Version 1.2026.728.100 and an Optimum (optonline.net) IMAP account.

This account previously worked correctly in New Outlook on this same PC.

The original problem was not authentication. New Outlook continued to receive mail normally, but read/delete actions performed in Outlook no longer synchronized back to the IMAP server. Changes made on other devices synchronized into Outlook correctly.

To correct the one-way synchronization issue, I removed the account and attempted to add it again.

Since then, New Outlook consistently displays:

"Something went wrong. Try again. You may need an app password."

The provider (Optimum) does not support app passwords.

I have verified that the same credentials work successfully with:

• Optimum Webmail
• Apple Mail on iPhone and iPad
• Outlook for iOS

The IMAP settings are:

• IMAP: mail.optimum.net, port 993, SSL/TLS
• SMTP: mail.optimum.net, port 465, SSL/TLS

Entering an intentionally incorrect password produces the same error message as the correct password.

Other IMAP accounts continue to work normally in the same installation of New Outlook.

This appears to be the same New Outlook IMAP issue described in this thread

Answer 1

@seth scott said

This appears to be the same New Outlook IMAP issue described in this thread

Your link didn't make it into the post. Are any of these what you were refereeing to?
https://learn.microsoft.com/en-us/answers/questions/5944655/emails-not-being-sent-using-outlook-classic-for-op https://learn.microsoft.com/en-us/answers/questions/4636987/trying-for-2-days-to-add-my-optonline-maill-accoun

Since you have confirmed the server settings and password using another client, not much left to try.

1 -- Worth a shot, but not likely a fix.

Nuke your New Outlook for Windows Profile and start all over. (Not everything gets removed when you just remove an account or uninstall the app).

If Outlook still has the account under View -> View settings -> Accounts > Your accounts:

• Pick the Account and [Manage]
• [Remove]
• (o) Remove from all devices (If you see it)

Then to Nuke the profile see the answer by "Hornblower409 Dec 11, 2025" in
https://learn.microsoft.com/en-us/answers/questions/5655980/outlook-starting-error-repair-reinstall-reset-does

2 -- As suggested by one of the other Optimum reports:

Create a new (NON OPTIMUM) email address that will load onto your Outlook, then open your optimum account through your browser, locate preferences, and select "Mail Forwarding". Enter your newly created email address in the specified field and you will now get your Optimum mail through your Outlook App.