Docker
Changing a parameter in Passwork
Open the desktop version of Passwork and go to Settings and Users → System Settings → Global → Email service.
Enable the Send notifications to email option, choose Local service and specify the sender's email, then save the changes:

Configuring and changing settings in Postfix
Configuring the SMTP sender address
Open or create a file at /<passwork>/conf/postfix/sasl_passwd
nano /<passwork>/conf/postfix/sasl_passwd
Add an SMTP address with the sender's user login and password:
[mail.isp.example] [email protected]:password
Example of using a non-standard TCP port:
[mail.isp.example]:587 [email protected]:password
Example of using Gmail:
[smtp.gmail.com]:587 [email protected]:password
Create a hashed database for Postfix:
docker exec -it passwork_postfix postmap /etc/postfix/sasl_passwd
Afterwards, the Postfix sasl_passwd.db database will be located at /<passwork>/conf/postfix/.
Restrict access to data files
The files created contain SMTP credentials in plain text. For security reasons, access should be restricted so that only the root user can read and write to them.
Assign rights to the owner and set the root user as the owner:
chown root:root /<passwork>/conf/postfix/sasl*
chmod 0600 /<passwork>/conf/postfix/sasl*
Configuring Postfix as a server relay (container)
Edit the configuration file at /<passwork>/conf/postfix/main.cf:
nano /<passwork>/conf/postfix/main.cf
Add and edit the following parameters:
# Specify the FQDN name of the server
myhostname = hostname.passwork.local
# Specify the parameter to your SMTP server from the "Configuring the SMTP sender address" step
relayhost = [mail.isp.example]:587
# Add authentication enable parameters at the end of the file
smtp_sasl_auth_enable = yes
smtp_sasl_security_options = noanonymous
smtp_sasl_password_maps = hash:/etc/postfix/sasl_passwd
smtp_use_tls = yes
smtp_tls_CAfile = /etc/ssl/certs/ca-certificates.crt
Save the changes and restart the Postfix service:
docker exec -i passwork_postfix service postfix reload