Docker
Open Passwork web interface and go to Settings and Users → System Settings → Notifications.
Activate the Send email notifications option and in Email service use Local service, specify the sender's email and save the changes:

Open or create a file at /<passwork>/conf/postfix/sasl_passwd
Add an SMTP address with the sender's user login and password:
Example of using a non-standard TCP port:
Example of using Gmail:
Create a hashed database for Postfix:
Afterwards, the Postfix sasl_passwd.db database will be located at /<passwork>/conf/postfix/.
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:
Edit the configuration file at /<passwork>/conf/postfix/main.cf:
Add and edit the following parameters:
Save the changes and restart the Postfix service: