Sendmail fail or success problem

Hi there,

Ubuntu + Apache + Sendmail

Send mail success:

Apr 24 21:05:26 www sm-mta[13104]: STARTTLS=client, relay=mail.domain.com., version=TLSv1/SSLv3, verify=FAIL, cipher=CAMELLIA256-SHA, bits=256/256

Apr 24 21:05:26 www sm-mta[13104]: r3P45QUM013102: to=<c1@domain.com>, delay=00:00:00, xdelay=00:00:00, mailer=esmtp, pri=120975, relay=mail.domain.com. [xx.xx.xx.xx], dsn=2.0.0, stat=Sent (OK id=1UVDR0-0001Mk-Rt)

Send mail failed:

Apr 24 21:12:10 www sm-mta[13117]: STARTTLS=client, relay=mail.domain.com., version=TLSv1/SSLv3, verify=FAIL, cipher=CAMELLIA256-SHA, bits=256/256

Apr 24 21:12:11 www sm-mta[13117]: r3O9uaIJ008639: to=<c2@domain.com>, ctladdr=<www-data@www.domain.com> (33/33), delay=18:15:35, xdelay=00:00:03, mailer=esmtp, pri=10021426, relay=mail.domain.com. [xx.xx.xx.xx], dsn=4.3.0, stat=Deferred: 451 Temporary local problem - please try later

Help!

Is there any wrong config?

Thanks.