dovecot + sieve: message recovery possible after rule pointed to invalid mailbox?

[dovecot at ptld.com]

> error: msgid=<433788c81ea044c4ae49cb39a6f673f3 at ALB-DC-EXC08.CLPL.INTERN>: failed to store into mailbox 'ABC': Internal error occurred. Refer to server log for more information. [2022-04-28
> 07:41:10].
> 
> Which "server log" is meant in this error message? 


This would be your mail logs, usually somewhere inside of /var/log/ depending on your distro. 
Sometimes in /var/log/messages or /var/log/maillog or other.