If I had installed Postal from a package latest.tgz would it be possible to safely upgrade it to the latest version of the repository by git pull?
I believe so, as long as the normal upgrade steps (bundle, database migrations, etc) are followed. It's worth noting that due to a recent upgrade of Rails, libffi-dev is now a system dependency, so you may wish to install this before upgrading. Update this ticket if you have any trouble with it.
I have just prepared myself to upgrade process :) One more thing before I start. Initially postal was installed from a package latest.tgz. Now I am going to upgrade it to master branch from GitHub. What is the correct path for the contents of postal-master.zip? Should it be /opt/postal/app or /opt/postal/app/postal-master subfolder? This is the cause of that the command wget https://postal.atech.media/packages/stable/latest.tgz -O - | sudo -u postal tar zxpv -C /opt/postal/app puts the archive's content to /opt/postal/app/latest.
As a matter of fact upgrade completed successfully. 馃憤
Your /opt/postal/app directory should look like the following when you're done:

Did you also run postal bundle /opt/postal/vendor/bundle and postal upgrade?
Did you also run postal bundle /opt/postal/vendor/bundle and postal upgrade?
Exactly. Everything was ok and Postal started normally.
Most helpful comment
I believe so, as long as the normal upgrade steps (bundle, database migrations, etc) are followed. It's worth noting that due to a recent upgrade of Rails, libffi-dev is now a system dependency, so you may wish to install this before upgrading. Update this ticket if you have any trouble with it.