SendMail 是否支持出站 TLS 加密而不添加到 sendmail.mc 文件？

CentOS 5.x

SendMail 是否支持“開箱即用”的機會性 TLS？

我習慣於將以下內容顯式添加到 /etc/mail/sendmail.mc

define(`confAUTH_MECHANISMS’, `LOGIN PLAIN’)dnl
define(`confCACERT_PATH’,`/etc/pki/tls/certs’)dnl
define(`confCACERT’,` /etc/pki/tls/certs/intermediates.crt’)dnl
define(`confSERVER_CERT’,` /etc/pki/tls/certs/tls-cert-public.pem’)dnl
define(`confSERVER_KEY’,` /etc/pki/tls/certs/tls-cert-private.key‘)dnl
define(`confCLIENT_CERT’,` /etc/pki/tls/certs/tls-cert-public.pem‘)dnl
define(`confCLIENT_KEY’,` /etc/pki/tls/certs/tls-cert-private.key‘)dnl

然而，它似乎像出站 TLS 一樣工作，而不必在那裡。我在傳遞日誌中註意到以下內容：

Mar  4 04:36:08 bob sendmail[23831]: q29Ja84u011122: from=<example@foo.com>, size=3262, class=0, nrcpts=1, msgid=<CA3B625A9CDFA44B811445BB84BDD45C9799A2@exch.foo.com>, proto=ESMTP, daemon=MTA, relay=exch.foo.com [192.168.0.1]
Mar  4 04:36:08 bob sendmail[23834]: STARTTLS=client, relay=mx.remotefoo.com., version=TLSv1/SSLv3, verify=FAIL, cipher=AES128-SHA, bits=128/128
Mar  4 04:36:08 bob sendmail[23834]: q29Ja84u011122: to=<recipient@remotefoo.com>, delay=00:00:00, xdelay=00:00:00, mailer=esmtp, pri=123262, relay=mx.remotefoo.com. [12.13.14.15], dsn=4.0.0, stat=Deferred: Connection reset by mx.remotefoo.com.

IP、電子郵件地址和主機名已重命名以保護無辜者。=）中間線讓我感到困惑。我希望只有在 sendmail 實際使用 TLS 時才能看到這一點。

這可能嗎？如果是這樣，用於此的公鑰/私鑰在哪裡？

更新

我正在重新審視這個問題，因為我仍然很好奇。這是完整的 sendmail.mc（更改 IP 以保護無辜者）：

divert(-1)
#
# DO NOT EDIT THIS FILE.  It is managed by the appliance node manager
# or create_smtp_profile script.  Any changes you make may be
# overwritten.
#
divert(0)
dnl #
dnl # This is the sendmail macro config file for m4. If you make changes to
dnl # /etc/mail/sendmail.mc, you will need to regenerate the
dnl # /etc/mail/sendmail.cf file by confirming that the sendmail-cf package is
dnl # installed and then performing a
dnl #
dnl #     make -C /etc/mail
dnl #
include(`/usr/share/sendmail-cf/m4/cf.m4')dnl
VERSIONID(`setup for linux-gnu')dnl
OSTYPE(`linux-gnu')dnl
dnl #
dnl # Disable DNS lookups
FEATURE(`nocanonify')dnl
define(`confBIND_OPTS',`-DNSRCH -DEFNAMES')dnl
dnl #
dnl # default logging level is 9, you might want to set it higher to
dnl # debug the configuration
dnl #
dnl define(`confLOG_LEVEL', `9')dnl
define(`confLOG_LEVEL', `9')dnl

dnl #
dnl # Uncomment and edit the following line if your outgoing mail needs to
dnl # be sent out through an external mail server:
dnl #

dnl #
dnl # Uncomment and edit the following line if your incoming mail needs to
dnl # be sent to an internal mail server:
dnl #
dnl define(`MAIL_HUB',`smtp.your.provider')dnl
dnl FEATURE(`stickyhost')dnl
dnl #
define(`confDOMAIN_NAME', `subdomain.support.foo.com')dnl
define(`confDEF_USER_ID',``8:12'')dnl
dnl define(`confAUTO_REBUILD')dnl
define(`confTO_CONNECT', `1m')dnl
define(`confTRY_NULL_MX_LIST',true)dnl
define(`confDONT_PROBE_INTERFACES',true)dnl
define(`PROCMAIL_MAILER_PATH',`/usr/bin/procmail')dnl
define(`ALIAS_FILE', `/etc/aliases')dnl
define(`STATUS_FILE', `/var/log/mail/statistics')dnl
define(`UUCP_MAILER_MAX', `2000000')dnl
define(`confUSERDB_SPEC', `/etc/mail/userdb.db')dnl
define(`confPRIVACY_FLAGS', `authwarnings,novrfy,noexpn,restrictqrun')dnl
define(`confAUTH_OPTIONS', `A')dnl
dnl #
dnl # The following allows relaying if the user authenticates, and disallows
dnl # plaintext authentication (PLAIN/LOGIN) on non-TLS links
dnl #
dnl define(`confAUTH_OPTIONS', `A p')dnl
dnl #
dnl # PLAIN is the preferred plaintext authentication method and used by
dnl # Mozilla Mail and Evolution, though Outlook Express and other MUAs do
dnl # use LOGIN. Other mechanisms should be used if the connection is not
dnl # guaranteed secure.
dnl # Please remember that saslauthd needs to be running for AUTH.
dnl #
dnl TRUST_AUTH_MECH(`EXTERNAL DIGEST-MD5 CRAM-MD5 LOGIN PLAIN')dnl
dnl define(`confAUTH_MECHANISMS', `EXTERNAL GSSAPI DIGEST-MD5 CRAM-MD5 LOGIN PLAIN')dnl
dnl #
dnl # Rudimentary information on creating certificates for sendmail TLS:
dnl #     cd /usr/share/ssl/certs; make sendmail.pem
dnl # Complete usage:
dnl #     make -C /usr/share/ssl/certs usage
dnl #
dnl define(`confCACERT_PATH',`/usr/share/ssl/certs')
dnl define(`confCACERT',`/usr/share/ssl/certs/ca-bundle.crt')
dnl define(`confSERVER_CERT',`/usr/share/ssl/certs/sendmail.pem')
dnl define(`confSERVER_KEY',`/usr/share/ssl/certs/sendmail.pem')
dnl #
dnl # This allows sendmail to use a keyfile that is shared with OpenLDAP's
dnl # slapd, which requires the file to be readble by group ldap
dnl #
dnl define(`confDONT_BLAME_SENDMAIL',`groupreadablekeyfile')dnl
dnl #
dnl define(`confTO_QUEUEWARN', `4h')dnl
dnl define(`confTO_QUEUERETURN', `5d')dnl
define(`confQUEUE_LA', `50')dnl
define(`confREFUSE_LA', `50')dnl
define(`confTO_IDENT', `0')dnl
dnl FEATURE(delay_checks)dnl
FEATURE(`no_default_msa',`dnl')dnl
FEATURE(`smrsh',`/usr/sbin/smrsh')dnl
FEATURE(`mailertable',`hash -o /etc/mail/mailertable.db')dnl
FEATURE(`virtusertable',`hash -o /etc/mail/virtusertable.db')dnl
FEATURE(redirect)dnl
FEATURE(always_add_domain)dnl
FEATURE(use_cw_file)dnl
FEATURE(use_ct_file)dnl
dnl #
dnl # The following limits the number of processes sendmail can fork to accept
dnl # incoming messages or process its message queues to 12.) sendmail refuses
dnl # to accept connections once it has reached its quota of child processes.
dnl #
dnl define(`confMAX_DAEMON_CHILDREN', 12)dnl
dnl #
dnl # Limits the number of new connections per second. This caps the overhead
dnl # incurred due to forking new sendmail processes. May be useful against
dnl # DoS attacks or barrages of spam. (As mentioned below, a per-IP address
dnl # limit would be useful but is not available as an option at this writing.)
dnl #
dnl define(`confCONNECTION_RATE_THROTTLE', 3)dnl
dnl #
dnl # The -t option will retry delivery if e.g. the user runs over his quota.
dnl #
FEATURE(local_procmail,`',`procmail -t -Y -a $h -d $u')dnl
FEATURE(`access_db',`hash -T<TMPF> -o /etc/mail/access.db')dnl
FEATURE(`blacklist_recipients')dnl
define(`confDOUBLE_BOUNCE_ADDRESS', `')dnl
EXPOSED_USER(`root')dnl
dnl #
dnl # The following causes sendmail to only listen on the IPv4 loopback address
dnl # 127.0.0.1 and not on any other network devices. Remove the loopback
dnl # address restriction to accept email from the internet or intranet.
dnl #
DAEMON_OPTIONS(`Port=smtp,Addr=127.0.0.1, Name=MTA, InputMailFilters=')dnl
DAEMON_OPTIONS(`Port=smtp, Addr=192.168.1.1,Name=MTA,Modifiers=b,InputMailFilters=')dnl
CLIENT_OPTIONS(`Family=inet, Addr=192.168.1.1')dnl

dnl #
dnl # The following causes sendmail to additionally listen to port 587 for
dnl # mail from MUAs that authenticate. Roaming users who can't reach their
dnl # preferred sendmail daemon due to port 25 being blocked or redirected find
dnl # this useful.
dnl #
dnl DAEMON_OPTIONS(`Port=submission, Name=MSA, M=Ea')dnl
dnl #
dnl # The following causes sendmail to additionally listen to port 465, but
dnl # starting immediately in TLS mode upon connecting. Port 25 or 587 followed
dnl # by STARTTLS is preferred, but roaming clients using Outlook Express can't
dnl # do STARTTLS on ports other than 25. Mozilla Mail can ONLY use STARTTLS
dnl # and doesn't support the deprecated smtps; Evolution <1.1.1 uses smtps
dnl # when SSL is enabled-- STARTTLS support is available in version 1.1.1.
dnl #
dnl # For this to work your OpenSSL certificates must be configured.
dnl #
dnl DAEMON_OPTIONS(`Port=smtps, Name=TLSMTA, M=s')dnl
dnl #
dnl # The following causes sendmail to additionally listen on the IPv6 loopback
dnl # device. Remove the loopback address restriction listen to the network.
dnl #
dnl DAEMON_OPTIONS(`port=smtp,Addr=::1, Name=MTA-v6, Family=inet6')dnl
dnl #
dnl # enable both ipv6 and ipv4 in sendmail:
dnl #
dnl DAEMON_OPTIONS(`Name=MTA-v4, Family=inet, Name=MTA-v6, Family=inet6')
dnl #
dnl # We strongly recommend not accepting unresolvable domains if you want to
dnl # protect yourself from spam. However, the laptop and users on computers
dnl # that do not have 24x7 DNS do need this.
dnl #
FEATURE(`accept_unresolvable_domains')dnl
dnl #
dnl FEATURE(`relay_based_on_MX')dnl
dnl #
dnl # Also accept email sent to "localhost.localdomain" as local email.
dnl #
LOCAL_DOMAIN(`localhost.localdomain')dnl
dnl #
dnl # The following example makes mail from this host and any additional
dnl # specified domains appear to be sent from mydomain.com
dnl #
dnl MASQUERADE_AS(`mydomain.com')dnl
dnl #
dnl # masquerade not just the headers, but the envelope as well
dnl #
dnl FEATURE(masquerade_envelope)dnl
dnl #
dnl # masquerade not just @mydomainalias.com, but @*.mydomainalias.com as well
dnl #
dnl FEATURE(masquerade_entire_domain)dnl
dnl #
dnl MASQUERADE_DOMAIN(localhost)dnl
dnl MASQUERADE_DOMAIN(localhost.localdomain)dnl
dnl MASQUERADE_DOMAIN(mydomainalias.com)dnl
dnl MASQUERADE_DOMAIN(mydomain.lan)dnl



MAILER(smtp)dnl
MAILER(procmail)dnl

我還收集了一個數據包擷取並確認伺服器確實正在啟動與外部方的 TLS 連接。

更新#2

我將日誌記錄一路加速 (99) 並向 gmail 帳戶發送了一條測試消息。我注意到有趣的細節：

Jun  6 12:55:10 foobox sendmail[1663]: r56Jsk7N001660: SMTP outgoing connect on foobox.foo.com
Jun  6 12:55:10 foobox sendmail[1663]: STARTTLS: ClientCertFile missing
Jun  6 12:55:10 foobox sendmail[1663]: STARTTLS: ClientKeyFile missing
Jun  6 12:55:10 foobox sendmail[1663]: STARTTLS: CACertPath missing
Jun  6 12:55:10 foobox sendmail[1663]: STARTTLS: CACertFile missing
Jun  6 12:55:10 foobox sendmail[1663]: STARTTLS: CRLFile missing
Jun  6 12:55:10 foobox sendmail[1663]: STARTTLS=client, init=1
Jun  6 12:55:10 foobox sendmail[1663]: STARTTLS=client, start=ok
Jun  6 12:55:10 foobox sendmail[1663]: STARTTLS=client, info: fds=10/9, err=2
Jun  6 12:55:10 foobox sendmail[1663]: STARTTLS=client, info: fds=10/9, err=2
Jun  6 12:55:10 foobox sendmail[1663]: STARTTLS=client, get_verify: 20 get_peer: 0x8907258
Jun  6 12:55:10 foobox sendmail[1663]: STARTTLS=client, relay=gmail-smtp-in.l.google.com., version=TLSv1/SSLv3, verify=FAIL, cipher=RC4-SHA, bits=128/128
Jun  6 12:55:10 foobox sendmail[1663]: STARTTLS=client, cert-subject=/C=US/ST=California/L=Mountain+20View/O=Google+20Inc/CN=mx.google.com, cert-issuer=/C=US/O=Google+20Inc/CN=Google+20Internet+20Authority, verifymsg=unable to get local issuer certificate
Jun  6 12:55:10 foobox sendmail[1663]: STARTTLS=read, info: fds=10/9, err=2
Jun  6 12:55:10 foobox last message repeated 3 times
Jun  6 12:55:10 foobox sendmail[1663]: STARTTLS=write, info: fds=10/9, err=3
Jun  6 12:55:10 foobox last message repeated 3 times
Jun  6 12:55:10 foobox sendmail[1663]: STARTTLS=read, info: fds=10/9, err=2
Jun  6 12:55:10 foobox sendmail[1663]: r56Jsk7N001660: to=<footestuser@gmail.com>, delay=00:00:07, xdelay=00:00:00, mailer=esmtp, pri=120015, relay=gmail-smtp-in.l.google.com. [74.125.129.27], dsn=2.0.0, stat=Sent (OK 198738510 s9si492345031pan.259 - gsmtp)

我可以確認我看到的是同一件事，獨立；未配置證書的sendmail安裝在發送到宣傳自己支持該協議的伺服器時仍然利用 TLS。

為了看看發生了什麼，我在tcpdump -n -n -w /tmp/pax.dump port 25 and host 178.18.123.145發送伺服器上執行了一個數據包擷取，然後將該數據包轉儲輸入到wireshark，它告訴我：

請注意突出顯示的數據包（第 17 號）如何包含證書資訊，前四個數據包（第 13 號）也是如此。數據包 13 是伺服器的證書，帶有信任鏈，“證書長度”為 2327 字節。這是客戶端的證書，長度為零字節（數據包分解視窗中突出顯示的行）。所以我認為有很好的證據表明 sendmail 會為客戶端生成一個隨機密鑰對，並為其提供零長度證書。

如果您發現這種行為很煩人，就像我一樣，您可以關閉它以便與所有主機進行通信，方法是

Try_TLS:                NO

在/etc/mail/access和再生access.db。

引用自：https://serverfault.com/questions/369343