Please check if you are able to connect that account through this Microsoft tool.
This tool should be able to tell us whether the problem is on Mailead's side, or whether there's something going on with the accounts themselves.
Please send a screenshot of the results page to our email support, and we'll try our best to help you resolve the issue.
IMAP host for Google should be imap.gmail.com, and for other providers, you can most of the time find them on the provider's website, or directly from your webmail.