There is "NewMail FIFO Path" configuration option in alpine. Quoting the help:

You may have Alpine create a FIFO special file (also called a named pipe) where it will send a one-line message each time a new message is received in the current folder, the INBOX, or any open Stayopen Folders. To protect against two different Alpines both writing to the same FIFO, Alpine will only create the FIFO and write to it if it doesn't already exist.

So, I set the option to '/tmp/alpine.fifo', and wrote simple utility to read messages from the FIFO and invoke 'notify-send':

#include <stdio.h>
#include <stdlib.h>
#include <errno.h>
#include <string.h>
#include <fcntl.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <unistd.h>

#define FIFO_NAME "/tmp/alpine.fifo"

int main(void)
{   
    char s[512];
    char cmd[512];
    int num;
    int fd = open(FIFO_NAME, O_RDONLY);
    do {
        if ((num = read(fd, s, 300)) == -1)
            perror("read");
        else {
            s[num] = '\0';
            sprintf(cmd, "notify-send -t 0 'New mail:' '%s'", s);
            system(cmd);
        }
    } while (num > 0);

    return 0;
}

Save it to alpine-notifier.c, and compile with 'gcc alpine-notifier.c -o alpine-notifier' command. Start 'alpine-notifier' after alpine is started. Enjoy pop-up notifications.

Postfix: simple mailing list

Have you tried to create owner-project23@server.tld entry in virtual maps?

As I understand It should make postfix change envelope sender ("send bounces to") address of messages send to project23@server.tld and fix your problem.

http://www.postfix.org/VIRTUAL_README.html#mailing_lists