Every step below is from an official source
Switch from Yahoo Mail to Proton Mail
What to do at Yahoo Mail before you leave, what Proton Mail needs when you join, and everything else the switch touches. Your full plan is built in your browser and stays there.
Official sources reviewed . How we review sources
At Yahoo Mail, before you leave
Download your Yahoo mail with an IMAP appBefore
Use Yahoo's IMAP settings to download your mail into an app like Thunderbird, Outlook or Mac Mail. Large accounts can take several days or longer.
Download your email from Yahoo Mail with IMAPYahoo. ReviewedChoose to keep mail on the serverDuring
If your email app asks whether to keep mail on the server, select yes. Otherwise your email is deleted from your Yahoo account as it downloads.
Download your email from Yahoo Mail with IMAPYahoo. ReviewedDownload what you need before closingAfter
Closing your Yahoo account removes access to your Yahoo Mail messages and folders, so download anything you want first. In most countries you can reactivate by signing in within 30 days.
Close or reactivate your Yahoo accountYahoo. Reviewed
At Proton Mail, when you join
Start Easy Switch in Proton Mail settingsDuring
Sign in at mail.proton.me and go to Settings, All settings, Import via Easy Switch. It imports email from Gmail, Yahoo Mail, Outlook or any IMAP provider. Some providers also allow calendars and contacts.
How to migrate to Proton using Easy SwitchProton. ReviewedCreate a Yahoo app password firstBefore
To import from Yahoo Mail, first generate a Yahoo app password for Easy Switch to use.
How to migrate to Proton using Easy SwitchProton. ReviewedChoose how far back to importDuring
You can import all messages or only the last 12 months, 3 months or month. Imports start with the newest messages, and you can run one transfer at a time from the same account.
How to migrate to Proton using Easy SwitchProton. Reviewed
Then: everything else the switch affects
The steps above are what Yahoo Mail and Proton Mail say. Your full checklist adds the accounts, codes, payments and devices that depend on your email provider, in a safe order. It's built from your answers, in your browser.