Hi, I had the same problem and I tracked it down to the following:
- The cron tries to connect to the database - this fails
- The croak wants to send an e-mail about that the database connection has failed
- It looks up the from-email in the database, which obviously does not work
- it uses '@' instead, which does not work either due to e-mail validation.
However, the main reason is that it cannot connect to the database. On my system the error was that I defined 'localhost' which has been resolved to ::1 and IPv6 does not seem to work. Defining 127.0.0.1 as DB host solved the problem for me. However, it's still funny that the system tries to look up something in the database to send an e-mail when the database does not work 😉
P.S. in my case it was a very old installation too (about 5 yrs), the error occured after moving to a new host with ipv6.