Every step below is from an official source
Switch from Gmail to Proton Mail
What to do at Gmail 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 Gmail, before you leave
Forward new Gmail messages to your new addressBefore
In Gmail settings, open the Forwarding and POP/IMAP tab and click Add a forwarding address. Click the verification link sent to the new address, then select Forward a copy of incoming mail to and save.
Expect only new mail to be forwardedDuring
Gmail forwards all new messages to the other account, except spam.
Download your mail and contacts with Google TakeoutBefore
Go to the Google Takeout page, choose which products to include, then select Create export. Contacts are exported as vCard.
How to download your Google data - Google Account HelpGoogle. ReviewedKnow that a removed Gmail address is retiredAfter
Download your data before removing Gmail. Gmail deletes your emails and settings after 30 days, and no one can use your Gmail address in the future.
Remove Gmail from your Google Account - Computer - Gmail HelpGoogle. 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 Gmail 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.