Send email with postfix on Ubuntu

This method consolidates common fixes from multiple tutorials and worked for me.

Install mailutils

sudo apt install mailutils

Configure username and password

sudo nano /etc/postfix/sasl_passwd

Input SMTP server, account and password.

[smtp.126.com]:465 username@126.com:password

The password of the 126 mailbox needs to generate an authorization code in the settings.
Then run postmap.

sudo chmod 600 /etc/postfix/sasl_passwd
sudo postmap /etc/postfix/sasl_passwd

Map sender

By default, postfix uses your username@hostname (the one you can see in the title bar of the Ubuntu Console window) to send emails. Such emails will be rejected by the smtp server (553 Mail from must equal authorized user), so you need to put it mapped to your real email address.

sudo nano /etc/postfix/generic

Write mapping.

root@ubuntu     username@126.com

Then run postmap.

sudo chmod 600 /etc/postfix/generic
sudo postmap /etc/postfix/generic

Modify the configuration file

sudo nano /etc/postfix/main.cf

edit relayhost.

relayhost = [smtp.126.com]:465

Add the following configuration at the end of the file.

# enable SASL authentication
smtp_sasl_auth_enable = yes

# disallow methods that allow anonymous authentication.
smtp_sasl_security_options = noanonymous

# where to find sasl_passwd
smtp_sasl_password_maps = hash:/etc/postfix/sasl_passwd

# where to find generic
smtp_generic_maps = hash:/etc/postfix/generic

# Enable STARTTLS encryption
smtp_use_tls = yes

# where to find CA certificates
smtp_tls_CAfile = /etc/ssl/certs/ca-certificates.crt

# Enable tls encryption
smtp_tls_wrappermode = yes
smtp_tls_security_level = encrypt

Note: Port 465 is SMTPS (implicit TLS). If you use port 587 instead, disable smtp_tls_wrappermode and use STARTTLS.

Send email

Then restart postfix and you can send emails.

sudo service postfix restart
echo "test" | mail -s "hello" target@126.com

View running log

If there is no response after running, see if there is any error in the log, so as to search and solve the problem in a targeted manner. You can open a separate terminal and place it next to it to view the log in real time.

tail -f /var/log/mail.log

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