为什么我的snedmail不稳定？

yzao

rh9＋apache2.0.49＋php4.3.5建立的论坛，发信调用php的mail函数，该函数调用sendmail发信。但是发信极其不稳定。请问高手如何解决？一下是发信不成功的日志文件,sendmail版本：sendmail-8.12.8-9.90
[code:1]Apr 24 22:09:04 HT sendmail[24635]: i3OE94PH024635: Authentication-Warning: localhost.localdomain: nobody set sender to [email protected] using -f
Apr 24 22:09:04 HT sendmail[24635]: i3OE94PH024635: [email protected], size=575, class=0, nrcpts=1, msgid=<[email protected]>, relay=nobody@localhost
Apr 24 22:09:04 HT sendmail[24638]: i3OE9444024638: from=<[email protected]>, size=814, class=0, nrcpts=1, msgid=<[email protected]>, proto=ESMTP, daemon=MTA, relay=HT [127.0.0.1]
Apr 24 22:09:04 HT sendmail[24635]: i3OE94PH024635: [email protected], [email protected] (99/-1), delay=00:00:00, xdelay=00:00:00, mailer=relay, pri=30343, relay=[127.0.0.1] [127.0.0.1], dsn=2.0.0, stat=Sent (i3OE9444024638 Message accepted for delivery)
Apr 24 22:09:09 HT sendmail[24640]: i3OE9444024638: to=<[email protected]>, delay=00:00:05, xdelay=00:00:05, mailer=esmtp, pri=30582, relay=m232.yeah.net. [202.108.45.232], dsn=5.0.0, stat=Service unavailable
Apr 24 22:09:09 HT sendmail[24640]: i3OE9444024638: i3OE9944024640: DSN: Service unavailable
Apr 24 22:09:14 HT sendmail[24640]: i3OE9944024640: to=<[email protected]>, delay=00:00:05, xdelay=00:00:05, mailer=esmtp, pri=31838, relay=m230.yeah.net. [202.108.45.230], dsn=5.6.0, stat=Data format error
Apr 24 22:09:14 HT sendmail[24640]: i3OE9944024640: i3OE9945024640: return to sender: Data format error
Apr 24 22:09:14 HT sendmail[24640]: i3OE9945024640: to=root, delay=00:00:00, xdelay=00:00:00, mailer=local, pri=32862, dsn=2.0.0, stat=Sent[/code:1]