Setting up email sending

create a backup of your postfix config: cp /etc/postfix/main.cf /etc/postfix/main_bak.cf
open /etc/postfix/main.cf

add the following rows (make sure none of the rows are duplicated)

#mydestination = $myhostname, server.local, localhost.local, , localhost # you can comment this out
relayhost = [smtp.mail.com]:465 # replace this domain with your mail server
smtp_use_tls = yes
smtp_sasl_auth_enable = yes
smtp_sasl_security_options = noanonymous
smtp_sasl_password_maps = hash:/etc/postfix/sasl_passwd
smtp_tls_CAfile = /etc/ssl/certs/ca-certificates.crt
smtp_tls_wrappermode = yes
smtp_tls_security_level = encrypt

# If your mail provider doesn't support ipv6, add/change this line
inet_protocols = ipv4

create this file: /etc/postfix/sasl_passwd with the following content:
```
[smtp.mail.com]:465    test@mail.com:PASSWD
```
make it only readable by your user: chmod 600 /etc/postfix/sasl_passwd
then: postmap /etc/postfix/sasl_passwd
install for passwd support: apt install libsasl2-modules
restart postfix: systemctl restart postfix.service

you can test it multiple ways:

echo "Test mail from postfix" | mail -s "Test Postfix" test@test.com
OR
echo "test" | /usr/bin/pvemailforward

logs can be found here:
- /var/log/mail.warn
- /var/log/mail.info

Common Issue:

If you can't send emails, because the domain in the FROM address is pointing to your server and the configured mail server rejects the mails with the following error:

Sender address rejected: Domain not found (in reply to RCPT TO command))

Then go to Datacenter -> Options -> Email from address and change it from root@$hostname to something that your mail server will accept.

Sources: