email [email protected] [BUG]

DA is always using the account username as default system mail account, because usernames are system accoutns (OS accounts). So this is not a bug but working as designed. If you are admin, the system main email account will be [email protected] by default.

You don't need to, since it already exists. Only difference is that this is a system account and not a virtual email account.
Hence you need to login with just admin as username and not [email protected] and this way you can use that email account. Same of all other username accounts on any domain.

So a bit more clear for the mail account [email protected]
username: admin
password: yourpass
server: mail.domain.com

For all other non-username accounts (in fact virtual email accounts):
username: [email protected]
password: yourpass
server: mail.domain.com

This way you can always use all email accounts.