Getting issue as “postdrop: warning: unable to look up public/pickup: No such file or directory”

We are using Alpine docker image 3.18 and we are doing SMTP installation and configuration to send mails. We are getting issue as “postdrop: warning: unable to look up public/pickup: No such file or directory”. Can someone guide us how to fix this issue

How are you installing it?

It seems you’re missing the postfix spool directories

I am installing by using “RUN apk add --no-cache postfix” command and then building Docker image and running Docker image.

Also, Copy is used to copy the SMTP config files. Below is the usage of command.
COPY postfix-main.cf /etc/postfix/main.cf
COPY ssmtp.conf_dev /etc/ssmtp/ssmtp.conf

It seems postfix spool directories are present. When we build the docker and login to container and do ls -l /var/spool/postfix/, i see public directory is present