Postfix/Dovecot NOQUEUE: reject | Relay access denied

I am having some trouble setting up an email server with postfix and dovecot. I have set up the config files but am getting the error:

Nov 22 23:49:09 server postfix/smtpd[31487]: connect from unknown[*.*.*.*]
Nov 22 23:49:09 server postfix/smtpd[31487]: NOQUEUE: reject: RCPT from unknown[*.*.*.*]: 454 4.7.1 <example@external.com>: Relay access denied; from=<example@internal.com> to=<example@external.com> proto=ESMTP helo=<[*.*.*.*]>
Nov 22 23:49:09 server postfix/smtpd[31487]: disconnect from unknown[*.*.*.*] ehlo=2 starttls=1 mail=1 rcpt=0/1 quit=1 commands=5/6

The server can successfully receive emails from external sources and send mail from the console.

Here is my postconf -n:

alias_database = hash:/etc/aliases
alias_maps = hash:/etc/aliases
append_dot_mydomain = no
biff = no
inet_interfaces = all
inet_protocols = all
mailbox_size_limit = 0
mydestination = localhost
myhostname = mail.example.com
mynetworks = 127.0.0.0/8 [::ffff:127.0.0.0]/104 [::1]/128
myorigin = /etc/mailname
readme_directory = no
recipient_delimiter = +
relayhost =
smtpd_banner = $myhostname ESMTP $mail_name (Ubuntu)
smtpd_relay_restrictions = permit_mynetworks,permit_sasl_authenticated,defer_unauth_destination
smtpd_tls_auth_only = yes
smtpd_tls_cert_file = /etc/letsencrypt/live/example.com/cert.pem
smtpd_tls_key_file = /etc/letsencrypt/live/example.com/privkey.pem
smtpd_use_tls = yes
virtual_alias_maps = mysql:/etc/postfix/mysql-virtual-alias-maps.cf
virtual_mailbox_domains = mysql:/etc/postfix/mysql-virtual-mailbox-domains.cf
virtual_mailbox_maps = mysql:/etc/postfix/mysql-virtual-mailbox-maps.cf
virtual_transport = lmtp:unix:private/dovecot-lmtp

I have tried various things with the smtpd recipient/relay restrictions, but nothing has worked. Any help would be greatly appreciated.