I keep looking into this.
This topic seems to indicate that there IS a process whereby MIAB would block sending the email at all: Blocked But Not Blacklisted - I am referring to @openletter 's comment.
I found the following line in /etc/postfix/main.cf :
smtpd_sender_restrictions=reject_non_fqdn_sender,reject_unknown_sender_domain,reject_authenticated_sender_login_mismatch,reject_rhsbl_sender dbl.spamhaus.org
I am not a coder. Is that a line of programming that will prevent MIAB from sending from a domain that is listed @ dbl.spamhaus.org? (which is where my problem domain has gotten listed).
If it is, how do I edit that line to turn that OFF? (and I’m guessing I would need to RE-edit that line every time I update MIAB).
The post I referred to says there are TWO places where sending can be blocked. Any of you wonderfully smart people know where the other one is?