In the real world: how many legitimate mail is blocked under these client and/or help restrictions?

[Gerben Wierda]

I was wondering, how many legitimate email (i.e. poorly configured but legit 
MTA’s out there) would be blocked with either of these?

unknown_client_reject_code = 550 # Hmm, should this be another value in the 5xx 
range?
smtpd_recipient_restrictions =
        …,
        reject_unknown_client_hostname
        ...


unknown_hostname_reject_code = 550 # Hmm, should this be another value in the 
5xx range?
smtpd_helo_restrictions = 
        …,
        reject_unknown_helo_hostname,
        …

I personally suspect that the reject_unknown_client_hostname would block too 
much, but the reject_unknown_helo_hostname would be ok. Am I right?

I’d like to turn this on against spam, but I don’t want to lose legit mail.

G