We are aware of issues affecting email functionality where a small subset of users may not be able to log into their accounts. Technical teams have been engaged and are investigating the issue as a priority.
As a workaround, clients are able to send and receive emails from their account(s) via webmail. Please use the following link for the knowledge article explaining how to do this.
https://www.uk2.net/knowledgebase/display/UK2/How+To+Log+Into+Webmail
Unfortunately, access to your old emails is only possible if you have previously configured and accessed your emails via any mail client (such as Outlook, Mail, Thunderbird, etc). but, you will not be able to send/receive from your client at this time.
We apologise for the inconvenience caused by this issue. If you have any other questions, please let us know and we will be happy to help!