Yep, this logics still weird. Workaround by using the main account authentication, but this will be security issued and shouldn't use from any 3rd party app.The new Exim setting is affecting to MDaemon usage. For example, we have some customers using one email account for authenticating for all outgoing emails. So, the email for authentication is different than the email in FROM field. With this type of customers, the new ACL will stop all outgoing emails.
Putting the setting "AUTH_BLOCK_SENDER_SPOOFING = no" into /etc/exim.variables.conf.custom will change the whole server. Is there any way to use it for a specific domain in the system?
If the main account ( without @domain ) can use to sproof any "{sender}@user_domain", then any sub email account must can sproof the "{sender}" with same "@domain" authentication too.