Vpopmail and people reaching their maildir quota

This tiny program lists all users of a domain with a maildir quota usage above 90%.

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>

#include <pwd.h>
#include <errno.h>

#include <vpopmail.h>
#include <vauth.h>

int main(int argc, char **argv) {
    struct vqpasswd *user;
    char dir[1024];
    uid_t uid;
    gid_t gid;
    int offset_counter = -1, sort = 1, usage;

    if (argc != 2) {
        fprintf(stderr, "Usage: %s <domain>n", argv[0]);
        return EXIT_FAILURE;
    }
    if (vget_assign(argv[1], NULL, 0, &uid, &gid) == NULL) {
        fprintf(stderr, "domain '%s' does not existn", argv[1]);
        return EXIT_FAILURE;
    }
    if (setgid(gid) || setuid(uid)) {
        fprintf(stderr, "could not setuid/setgid to %d:%dn", uid, gid);
        return EXIT_FAILURE;
    }

    while (NULL != (user = vauth_getall(argv[1], !++offset_counter, sort))) {
        if (strcmp(user->pw_shell, "NOQUOTA")) {
            snprintf(dir, sizeof(dir), "%s/Maildir", user->pw_dir);
            usage = vmaildir_readquota(dir,
                format_maildirquota(user->pw_shell));

            if (usage >= 90) {
                printf("%s %s %dn", user->pw_name, user->pw_shell, usage);
            }
        }
    }

    return EXIT_SUCCESS;
}