Spammers using server as a relay

I’m having a problem with spammers using my server to relay spam. I thought I had it fixed with my main.cf (code below). But apparently I did not. The from email on the spam is not any email in my system and the only reason thousands of emails didn’t go out is because I use sendinblue and it will only send out 300 emails a day then shut me off. I tried shutting down ports yesterday to see if that helped but it did not so I don’t understand how or where they’re getting in. After I changed the main.cf it stopped till last night but I guess that was a fluke… Also in the HELO section, if I have it as is I cannot send email from my Outlook 2013. It will spit a 504 5.2.2 error but once I remove reject_non_fqdn_helo_hostname, reject_invalid_helo_hostname, it’ll allow Outlook.

Main.cf

# See /usr/share/postfix/main.cf.dist for a commented, more complete version


# 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 (Ubuntu)
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

# /etc/postfix/main.cf
# Sender restrictions:
smtpd_sender_restrictions =
    permit_mynetworks,
    reject_non_fqdn_sender,
    reject_unknown_sender_domain,
    permit
    
  # /etc/postfix/main.cf
# HELO restrictions:
smtpd_delay_reject = yes
smtpd_helo_required = yes
smtpd_helo_restrictions =
    permit_mynetworks,
    reject_non_fqdn_helo_hostname,
    reject_invalid_helo_hostname,
    permit
    
    # /etc/postfix/main.cf
# Recipient restrictions:
smtpd_recipient_restrictions =
   reject_unauth_pipelining,
   reject_non_fqdn_recipient,
   reject_unknown_recipient_domain,
   permit_mynetworks,
   reject_unauth_destination,
   check_sender_access
         hash:/etc/postfix/sender_access,
   reject_rbl_client zen.spamhaus.org,
   reject_rbl_client bl.spamcop.net,
   check_policy_service unix:postgrey/socket,
   permit


# TLS parameters
smtpd_tls_cert_file = /etc/ssl/certs/ssl-cert-snakeoil.pem
smtpd_tls_key_file = /etc/ssl/private/ssl-cert-snakeoil.key
smtpd_tls_security_level = may

smtp_tls_CApath=/etc/ssl/certs
smtp_tls_security_level = may
smtp_tls_session_cache_database = btree:${data_directory}/smtp_scache

smtpd_relay_restrictions = permit_mynetworks permit_sasl_authenticated reject_unauth_destination
        
alias_maps = hash:/etc/aliases
alias_database = hash:/etc/aliases
myorigin = localhost
mydestination = localhost
mynetworks = 127.0.0.0/8 [::ffff:127.0.0.0]/104 [::1]/128
mailbox_size_limit = 0
recipient_delimiter = +
inet_protocols = all
virtual_alias_maps = hash:/etc/postfix/virtual
sender_bcc_maps = hash:/etc/postfix/bcc
sender_dependent_default_transport_maps = hash:/etc/postfix/dependent
mailbox_command = /usr/bin/procmail-wrapper -o -a $DOMAIN -d $LOGNAME
home_mailbox = Maildir/
smtpd_sasl_auth_enable = yes
broken_sasl_auth_clients = yes
smtpd_recipient_restrictions = permit_mynetworks permit_sasl_authenticated reject_unauth_destination
allow_percent_hack = no
tls_server_sni_maps = hash:/etc/postfix/sni_map
milter_default_action = accept
smtpd_milters = inet:localhost:8891
non_smtpd_milters = inet:localhost:8891
mynetworks_style = subnet

relayhost = [smtp-relay.sendinblue.com]:587

# outbound relay configurations
smtp_sasl_auth_enable = yes
smtp_sasl_password_maps = hash:/etc/postfix/sasl_passwd
smtp_sasl_security_options = noanonymous
smtp_tls_security_level = may
header_size_limit = 4096000
message_size_limit = 50000000
disable_vrfy_command = yes

|SYSTEM INFORMATION| |
|Virtualmin 6.17
PostFix 3.4.13|
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|OS type and version:| Ubuntu 20.04LTS |
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