From my Gmail account I ran the shuttlecloud import tool to import my yahoo mail. The process ran for about a day, but afterwards only my folders were migrated. My entire inbox (about 40,000 e-mails) was not migrated.
Also, while the e-mails were importing many valid e-mails were getting flagged by Gmail as spam, so I had to go into the spam folder in Gmail and manually move them out.
Sometimes Yahoo blocks access to e-mails in large folders. The best workaround is to move the untransferred messages from your Inbox into a new folder. Here are the steps:
1. Create a new folder in your Yahoo account. (e.g. “newest”)
2. Move some of the e-mails from your Inbox to the new folder you created in Step 1 above.
3. Start a new import.
If this process works, repeat until all of your e-mails have been transferred.