Download your email from Yahoo Mail with IMAP

Use the IMAP settings below to download your email from Yahoo Mail into a third-party email app, like Thunderbird, Outlook, or Mac Mail. For accounts with a lot of content, it can take several days or longer to download everything. If you need specific instructions to configure your app with our settings or to check the progress of your download, please reach out to the app developer.

We’ve updated our Terms of Service and Privacy Policy – You’ll need to review and accept the new Terms of Service and Privacy Policy to allow third-party email apps to access your Yahoo Mail account. If you haven’t already, sign into your account using a web browser to do so.
First, review the following

Keep a copy of your email in your account – If your app asks you if you want to “keep mail on the server” during setup, select “yes,” or your email will be deleted from your account when it’s downloaded.
Backing up your email? Some apps default to only download a preview or snippet of your emails until an email is opened. Make sure your app is set to download the full contents of your email for offline use.
Limitations for large folders – Folders containing upwards of 1 million or more emails will have issues downloading all the messages. To resolve this, move some of the email to a new folder in your account.

Then, use this info to configure your app

Incoming Mail (IMAP) Server

Server – export.imap.mail.yahoo.com
Port – 993
Requires SSL – Yes

Outgoing Mail (SMTP) Server

Server – smtp.mail.yahoo.com
Port – 465 or 587
Requires SSL – Yes
Requires authentication – Yes

Your login info

If you’re using Yahoo Account Key, generate an app password and use that for your account password.

Email address – Your full email address (name@domain.com)
Password – Your account’s password
Requires authentication – Yes

For some older email apps, you’ll need to adjust your account settings to grant it temporary access before the app will accept your password.

Fuente: https://en-global.help.yahoo.com/kb/new-mail-for-desktop/sln28681.html