And completed the MX transfer...

Now I'm trying to do the email migration but it's not working.

Despite knowing the correct login details...

I'm not sure what else to do?.. I've been though the migration steps in the help document.

The website DNS noe points to a new host (WP Engine) who recommended setting our business email up with you. So we've pointed that from our old host to Zoho. 

New emails come in fine.. but I'd like to keep our old ones at hand too.