MS Outlook / Office 365 / Live provides a free webmail service that allows an easy (easy here is perhaps subject to each own opinion) migration from Yahoo Mail, and possibly other providers as well. It does include moving (copying) all stored messages.
Caveat emptor: I have an Office 365 for Education account (which is free for the end users) and I am not sure if this is available for other licenses.
This can be achieved by setting up a Connected Account.
Connected accounts are typically used to enable your Office 365 email to receive mail sent to an email address that’s not hosted within your Office 365 environment. Connected accounts connect to the other email account via POP or IMAP. They differ from using forwarders from the other account, because connected accounts will download all of the existing email stored on the other mail server, as well as any future emails sent to it.
The above link provides detailed instructions. Below I will list a summary of the required steps, tailored for Yahoo Mail.
- Settings > Mail > Connected accounts
+ to add a new account
- Enter your email@example.com address
- You are supposed to enter your Yahoo Mail password; however type a wrong password (this is important —- see below)
- An error message will pop up, something like A secured connection couldn’t be established to this account.
- Click Skip
- Chose IMAP
- Enter your Yahoo Mail address and password (now the correct one)
- Server details:
imap.mail.yahoo.com, Basic authentication, SSL encryption, Port 993.
- Wait until the migration is completed. You will notice that is is completed by looking at the status in the Connected accounts list.
Step 4 is important because otherwise it will default to a POP3 connection, which will not migrate your folders, only the Inbox. Entering a wrong password (or wrong domain, like @yahoo.com.fake) would allow to setup an IMAP connection.
I did this process recently to migrate from Yahoo Mail to Outlook. I had > 26000 messages totaling about 6.5 GB. It took about 10 hours to complete.
After this process is completed, it will keep copying your messages from Yahoo Mail to Outlook. It will not sync in the other way back, i.e., if you delete a Yahoo message on Outlook, that message will remain in your Yahoo account.
I have yet to completely delete my Yahoo account, so I can't tell what would happen in that case; I assume the migrated Yahoo messages would remain in the Outlook account and an error would appear in the Connected accounts status.
Using a third party tool
I didn't try this one. Apparently there is this tool to convert from Yahoo Mail to Office 365. Although it is listed in a repo under Microsoft domain, I don't know how officially supported it is.