Null Client Mail Server

I want to set up a null client mail server, i.e. a mail server that sends e-mails, but does not receive e-mails. I tried multiple guides relying on postfix, checked discussions on this and other sites, and consulted the official postfix website. The server still does not send e-mails. The message submitted via the following line

echo "This is the body of an encrypted email" | mail -s "This is the subject line" [email protected]

where [email protected] is an e-mail address of mine that is not related to that server does not arrive. I already tried checked multiple recipient e-mail addresses. None of them receives a message.

The content of /etc/postfix/main.cf currently is

# 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

# TLS parameters
smtpd_tls_cert_file=/etc/letsencrypt/live/example.com/fullchain.pem
smtpd_tls_key_file=/etc/letsencrypt/live/example.com/privkey.pem
smtpd_tls_security_level=may
smtp_use_tls=yes
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 defer_unauth_destination
myhostname = someone.localdomain
alias_maps = hash:/etc/aliases
alias_database = hash:/etc/aliases
myorigin = $mydomain
mydestination =
relayhost = $mydomain
mynetworks = 127.0.0.0/8 [::1]/128
mailbox_size_limit = 0
recipient_delimiter = +
inet_interfaces = loopback-only
inet_protocols = ipv4
local_transport = error: local delivery disabled

Instead of example.com I use my actual domain.

On the DNS server, I only set an A record. Do I need a MX record? Do I need to set up a subdomain?

I configured the ufw to allow for postfix traffic: sudo ufw allow Postfix

This Ubuntu 20.04 machine also hosts a nginx web server.

What I would like to do is to send e-mails directly from the server using a shell script. I do not want to connect it to any program outside the server. The setup should be as secure as possible, blocking any incoming e-mails or attacks using the mail ports. I do not have a particular preference for postfix. It is simply the software that most guides use.

ด้วยเหตุผลบางอย่างที่คุณตั้งไว้

รีเลย์โฮสต์ = $โดเมนของฉัน

สิ่งนี้ไม่สมเหตุสมผล เนื่องจากคุณบอกว่าคุณกำลังพยายามส่งอีเมลขาออกไปยังปลายทางโดยตรง แทนที่จะส่งกลับมาที่ตัวคุณเอง แม้ว่าคุณจะพยายามส่งจดหมายทั้งหมดอีกครั้งในเครื่อง แต่นี่ก็ไม่ใช่วิธีที่จะทำ

เพียงลบบรรทัดนี้ออกจากการกำหนดค่าของคุณทั้งหมด