lib/mailer.lib.php 에 $fmail 에 해당 도메인명을 넣어 값을 고정하여 주십시오.

<?
if (!defined("_GNUBOARD_")) exit;

// 메일 보내기 (파일 여러개 첨부 가능)
// type : text=0, html=1, text+html=2
function mailer($fname, $fmail, $to, $subject, $content, $type=0, $file="", $cc="", $bcc="") 
{
    global $config;
    global $g4;

    // 메일발송 사용을 하지 않는다면
    if (!$config[cf_email_use]) return;

    $fname   = "=?$g4[charset]?B?" . base64_encode($fname) . "?=";
    $subject = "=?$g4[charset]?B?" . base64_encode($subject) . "?=";
    //$g4[charset] = ($g4[charset] != "") ? "charset=$g4[charset]" : "";

    $fmail = "admin@도메인명";

    $header  = "Return-Path: <$fmail>\n";
    $header .= "From: $fname <$fmail>\n";
    $header .= "Reply-To: <$fmail>\n";
    if ($cc)  $header .= "Cc: $cc\n";
    if ($bcc) $header .= "Bcc: $bcc\n";
    $header .= "MIME-Version: 1.0\n";
    //$header .= "X-Mailer: SIR Mailer 0.91 (sir.co.kr) : $_SERVER[SERVER_ADDR] : $_SERVER[REMOTE_ADDR] : $g4[url] : $_SERVER[PHP_SELF] : $_SERVER[HTTP_REFERER] \n";
    // UTF-8 관련 수정
    $header .= "X-Mailer: SIR Mailer 0.92 (sir.co.kr) : $_SERVER[SERVER_ADDR] : $_SERVER[REMOTE_ADDR] : $g4[url] : $_SERVER[PHP_SELF] : $_SERVER[HTTP_REFERER] \n";

    if ($file != "") {
        $boundary = uniqid("http://sir.co.kr/");

        $header .= "Content-type: MULTIPART/MIXED; BOUNDARY=\"$boundary\"\n\n";
        $header .= "--$boundary\n";
    }

    if ($type) {
        $header .= "Content-Type: TEXT/HTML; charset=$g4[charset]\n";
        if ($type == 2)
            $content = nl2br($content);
    } else {
        $header .= "Content-Type: TEXT/PLAIN; charset=$g4[charset]\n";
        $content = stripslashes($content);
    }
    $header .= "Content-Transfer-Encoding: BASE64\n\n";
    $header .= chunk_split(base64_encode($content)) . "\n";

    if ($file != "") {
        foreach ($file as $f) {
            $header .= "\n--$boundary\n";
            $header .= "Content-Type: APPLICATION/OCTET-STREAM; name=\"$f[name]\"\n";
            $header .= "Content-Transfer-Encoding: BASE64\n";
            $header .= "Content-Disposition: inline; filename=\"$f[name]\"\n";

            $header .= "\n";
            $header .= chunk_split(base64_encode($f[data]));
            $header .= "\n";
        }
        $header .= "--$boundary--\n";
    }
    @mail($to, $subject, "", $header, '-f'.$fmail);
}