Install and configure postfix on ubuntu

flowable config

flowable.mail.server.host=localhost
flowable.mail.server.port=25
flowable.mail.server.username=email
flowable.mail.server.password=password
flowable.mail.server.default-from=email

install and configure steps

Install Packages

# apt update

# apt install postfix mailutils -y

When asked, select "Satellite system"

Setup postfix and password database

# vim /etc/postfix/sasl_passwd

    Insert the line
    [smtp.mymail.com]:25 user@mymail.com:mysecretpassword

# postmap /etc/postfix/sasl_passwd

# ls -l /etc/postfix/sasl_passwd /etc/postfix/sasl_passwd.db

# rm /etc/postfix/sasl_passwd

# vim /etc/postfix/main.cf

    # specify SMTP relay host
    relayhost = [smtp.mymail.com]:587

    # 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
    
    ## for office 365
    smtp_use_tls = yes
    
    mydestination = $mydomain, localhost.$mydomain, localhost

# service postfix restart

Testing Your Postfix Configuration

echo  "body of your email" | mail -s "This is a subject" -a "From: you@example.com" recipient@elsewhere.com

Logs
/var/log/mail.log

Mail queue
mailq

Reprocess queue
postqueue -f

references

https://www.masterkenneth.com/2018/08/configuring-postfix-relay-for-mail-sending-ubuntu-16-04/

https://www.linode.com/docs/guides/postfix-smtp-debian7/

https://www.wirehive.com/thoughts/5-top-tips-reviewing-postfix-mail-queue/