Postfixadmin import with old server postfix users to new server

You can run postfixadmin-cli in a loop, for example (untested, but should work)

cat userlist.csv | IFS=';' while read mailbox password quota ; do
    postfixadmin-cli mailbox add "$mailbox" --password "$password" --password2 "$password" --quota "$quota"
done

This script assumes that your userlist.csv looks like this:

user@example.com;topsecret;100

Check postfixadmin-cli help for a list of available modules (not only mailboxes), and postfixadmin-cli mailbox add help for details about creating mailboxes.