Problem Self Hosted Mercury email server IMAP not able to login

Are there problems with login for a self-hosted email server?

Using the mail server Mercury from David Harris (pmail.com) it is not possible using erpnext to create email accounts as login to the IMAP server fails with unknown user or password

Login using a client like thunderbird does not give problems same is valid for Pegasus the email client

Any one have some advice?