Postfix - "Server configuration error."

I'm getting this error in my mail log:

Feb 29 21:06:14 mail postfix/smtpd[29464]: NOQUEUE: reject: RCPT from mail-vi1eur05olkn2106.outbound.protection.outlook.com[40.92.90.106]: 451 4.3.5 [email protected]: Recipient address rejected: Server configuration error; from=nicolo.****@hotmail.it [email protected] proto=ESMTP helo=<EUR05-VI1-obe.outbound.protection.outlook.com>

I recently installed rspamd and postgrey, but if I disable postgrey I get the same error.

This is my postfix config:

# See /usr/share/postfix/main.cf.dist for a commented, more complete version
smtpd_error_sleep_time = 1s
smtpd_soft_error_limit = 10
smtpd_hard_error_limit = 20

transport_maps = hash:/etc/postfix/transport

# Throttle limit policy mail (global)
smtp_destination_concurrency_limit = 4
polite_destination_rate_delay = 1s
smtp_extra_recipient_limit = 10

# Polite policy
polite_destination_concurrency_limit = 3
polite_destination_rate_delay = 1s
polite_destination_recipient_limit = 10

# Turtle policy
turtle_destination_concurrency_limit = 2
turtle_destination_rate_delay = 1s
turtle_destination_recipient_limit = 10
smtpd_sender_restrictions =
reject_unknown_sender_domain
permit_mynetworks
permit_sasl_authenticated
reject_unknown_reverse_client_hostname
smtpd_helo_required = yes
smtpd_helo_restrictions =
permit_mynetworks
permit_sasl_authenticated
check_helo_access hash:/etc/postfix/helo_access
reject_invalid_helo_hostname
reject_non_fqdn_helo_hostname
reject_unknown_helo_hostname
# Debian specific:  Specifying a file name will cause the first
# line of that file to be used as the name.  The Debian default
# is /etc/mailname.
#myorigin = /etc/mailname

smtpd_banner = $myhostname ESMTP $mail_name (Debian/GNU)
biff = no

# appending .domain is the MUA's job.
append_dot_mydomain = no

# Uncomment the next line to generate "delayed mail" warnings
#delay_warning_time = 4h

readme_directory = no

# See http://www.postfix.org/COMPATIBILITY_README.html -- default to 2 on
# fresh installs.
compatibility_level = 2

# TLS parameters
smtpd_tls_cert_file = /etc/letsencrypt/live/indst.eu/fullchain.pem
smtpd_tls_key_file = /etc/letsencrypt/live/indst.eu/privkey.pem
smtpd_use_tls=yes
smtpd_tls_session_cache_database = btree:${data_directory}/smtpd_scache
smtp_tls_session_cache_database = btree:${data_directory}/smtp_scache

# See /usr/share/doc/postfix/TLS_README.gz in the postfix-doc package for
# information on enabling SSL in the smtp client.
# Handing off local delivery to Dovecot's LMTP, and telling it where to store mail
virtual_transport = lmtp:unix:private/dovecot-lmtp

# Virtual domains, users, and aliases

smtpd_relay_restrictions = permit_mynetworks permit_sasl_authenticated check_relay_domains
myhostname = mail.indst.eu
alias_maps = hash:/etc/aliases
alias_database = hash:/etc/aliases
myorigin = indst.eu
mydestination = $myhostname, localhost.indst.eu, localhost
relayhost = 
mynetworks = 164.68.123.81 192.168.1.0/24 127.0.0.0/8
mailbox_size_limit = 0
recipient_delimiter = +
inet_interfaces = all
inet_protocols = ipv4
relay_domains = indst.eu
#home_mailbox = Maildir/
mailbox_command = 
smtpd_sasl_type = dovecot
smtpd_sasl_path = private/auth
smtpd_sasl_local_domain = 
smtpd_sasl_security_options = noanonymous
broken_sasl_auth_clients = yes
smtpd_sasl_auth_enable = yes
smtpd_recipient_restrictions =  permit_mynetworks, reject_sender_login_mismatch, permit_sasl_authenticated, reject_unauth_destination, reject_non_fqdn_recipient,  reject_non_fqdn_sender, reject_unknown_sender_domain, reject_unknown_recipient_domain, check_recipient_access hash:/etc/postfix/roleaccount_exceptions, check_sender_access hash:/etc/postfix/sender_access, reject_non_fqdn_hostname, reject_invalid_hostname, reject_unknown_reverse_client_hostname, reject_rbl_client zen.spamhaus.org, check_policy_service inet:127.0.0.1:10023, permit
smtp_tls_security_level = may
smtpd_tls_security_level = may
smtp_tls_note_starttls_offer = yes
smtp_use_tls=yes
smtpd_tls_loglevel = 1
smtpd_tls_received_header = yes
mail.indst.eu = mail.indst.eu
virtual_mailbox_domains = mysql:/etc/postfix/mysql-virtual-mailbox-domains.cf
virtual_mailbox_maps = mysql:/etc/postfix/mysql-virtual-mailbox-maps.cf
virtual_alias_maps = mysql:/etc/postfix/mysql-virtual-alias-maps.cf


maximal_queue_lifetime = 1d
delay_warning_time = 0h
bounce_template_file = /etc/postfix/bounce.cf
milter_protocol = 6
milter_mail_macros = i {mail_addr} {client_addr} {client_name} {auth_authen}
milter_default_action = accept
smtpd_milters = inet:127.0.0.1:11332
non_smtpd_milters = inet:127.0.0.1:11332

Thank you for your help.