How do I Import Gmail messages?

How do I Import Gmail messages?

I've tried downloading my mailbox contents from Google, but that gives me an mbox file when Zoho's import only takes .eml.

I've looked for tools to convert, but there are no free ones.

I've looked at pulling in my archived messages using Pop3, but get authentication errors (I've triple-checked my password and username). Google doesn't support migration to Zoho, and I can't find any information here on setting up Pop3 to import Gmail messages.

So what do I do? I feel like it shouldn't be this hard just to get my old emails into my new account.