Please first check whether the email account is listed in DH panel --> Mails --> Manage Email
If you see your email account in the list, you can click Edit to change the password.
To log in, you need to key in the full email address or the name next to the email address "nothing besides mxxxxxx".
It takes some time for the new emaill address to be valid. If you created email accounts yesterday, they should be working by now.
If the above is all correct, you can try to re-create some of the email accounts. If it still does not work, I can't think of any solution but to suggest you to contact DH support.
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