Reply by eMail SMTP authentication

I just did a fresh normal docker based setup and everything works so far.
I also added all those SMTP settings for sending out eMails like registration, or summary for a user.
Let’s name that account “talk

If I now want to add the feature “Reply by eMail” I therefore added a second mail account on my personal MailU instance with POP3 enabled.
Let’s name that account “repl

But: Now it seems the normal eMails also get “repl” as the sending address but use the smtp auth settings from user “talk”. And now my Mailserver denies that with some error 5xx for sure.

I did not find enough hints when is which address used and how would the “repl” account get any sending auth settings? I only found the POP3 setup stuff yet.

Until now it seems only to work if both addresses are the same account, but additional aliases.

I added one catch all reply+_%@mydomain which is the preferred syntax from mailu.