Allow exim to send FROM any catch-all address

Question

I have a domain shrimp.foo already setup at the MX to route all incoming mail addresses (*@shrimp.foo) to one particular mailbox the ISP provides for IMAP, POP, webmail, etc.: bubba@shrimp.foo

Tested sending TO random-address@shrimp.foo works.

Back on my Linux Ubuntu box, using the SMTP credentials, I can already send out mail as bubba@shrimp.foo, no problem.

Problem is, how do I send FROM an arbitrarily different address other than bubba@, but still the same domain somethingelse*@shrimp.foo*? My attempts using the mail command error:

Sender address rejected: not owned by user

In my /etc/exim4/passwd.client

# https://poczta.nazwa.pl/
shrimp.foo:bubba@shrimp.foo:password
*.shrimp.foo:bubba@shrimp.foo:password

Answer 1

Eventually I figured it out. Not sure which change mattered most for this but:

in /etc/exim4/update-exim4.conf.conf

dc_eximconfig_configtype='smarthost'
dc_smarthost='smtp.englishetc.pl::587' 

The ::587 wasn't obvious to me.

in /etc/exim4/passwd.client

# https://poczta.nazwa.pl/
englishetc.pl:bubba@englishetc.pl:passwd
smtp.englishetc.pl:bubba@englishetc.pl:passwd
^smtp[0-9]*.englishetc.pl:bubba@englishetc.pl:passwd
*.englishetc.pl:bubba@englishetc.pl:passwd