Setting up app passwords for IMAP (Gmail, Outlook, Yahoo)
Big providers ask for an app password for IMAP access. Here is how to create one at Gmail, Outlook and Yahoo.
What an app password is
An app password is a separate, single-purpose password you grant to one application — here: IMAP access for your migration. It works alongside two-step verification and you can revoke it afterwards without changing your main password.
Gmail and Outlook
Gmail: turn on two-step verification, go to your Google account → Security → App passwords and generate one for "Mail". Use imap.gmail.com, port 993.
Outlook/Microsoft 365: enable modern authentication, go to your account security settings and create an app password. Use outlook.office365.com, port 993.
Yahoo and other providers
Yahoo: go to Account security → Generate app password, choose "Other app" and note the password. Use imap.mail.yahoo.com, port 993.
With your own mail server or many smaller hosts an app password is not needed — there your regular mailbox password works for IMAP.