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making unverified_recipient_reject_code safe for temp errors

Dear Users,

we have the following in place:

smtpd_recipient_restrictions = reject_unknown_recipient_domain,
reject_unverified_recipient
unverified_recipient_reject_code = 550
unknown_address_reject_code = 550

today, we had an issue with our groupware so the following was happening:

NOQUEUE: reject: RCPT from unknown[ip]: 450 4.1.1 < ... at domain dot tld>:
Recipient address rejected: unverified address: Address verification in
progress; from=< ... at intmon01 dot int.domain.tld> to=< ... at domain dot tld>
proto=ESMTP helo=<intmai01.int.domain.tld>
Oct 11 17:19:13 kop01 postfix/lmtp[5711]: E759E301412: to=< ... at domain dot tld>,
relay=127.0.0.1[127.0.0.1]:2003, delay=13, delays=0/0.01/13/0, dsn=4.0.0,
status=undeliverable (host 127.0.0.1[127.0.0.1] refused to talk to me: 421
internal error: OpenResolveAddrFolder failed)
NOQUEUE: reject: RCPT from jir01.int.domain.tld[ip2]: 450 4.1.1
<demo. ... at domain dot tld>: Recipient address rejected: unverified address:
host 127.0.0.1[127.0.0.1] refused to talk to me: 421 internal error:
GetSession failed; from=< ... at domain dot tld> to=<demo. ... at domain dot tld>
proto=ESMTP helo=<jir01.int.domain.tld>

How do we reject unknown destinations / recipients still with a perm.
error, but be more robust against temp errors like the ones above?