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Sendmail.mc文件的最前面几行完成一些辅助工作，

divert(-1)dnl

在生成配置文件时删除额外的输出。

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

将sendmail所需的规则包含进来。

VERSIONID(`setup for Red Hat Linux’)dnl

指出配置文件是针对Red Hat Linux，（可以任意值）

OSTYPE(`linux’)dnl

必须设置为linux以获得sendmail所需文件的正确位置。

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 define(`SMART_HOST’,`smtp.your.provider’)

指定邮件服务器中继。

dnl #

define(`confDEF_USER_ID’,“8:12”)dnl

指定以mail用户（UID:8）和mail组（GID:12）的身份运行守护进程。

Define(`confTRUSTED_USER`，`SMMSP`) dnl

将smmsp添加到sendmail的可信用户列表中，其他的可信用户是root，uucp，daemon（smmsp用户被赋予部分sendmail假脱机目录和邮件数据库文件的所有权。

dnl define(`confAUTO_REBUILD’)dnl

如果有必要，sendmail将自动重建别名数据库。

define(`confTO_CONNECT’, `1m’)dnl

将sendmail等待初始连接完成的时间设置为1分钟（1m）

define(`confTRY_NULL_MX_LIST’,true)dnl

设为true，如果接收服务器是一台主机最佳的MX，试着直接连接那台主机。

define(`confDONT_PROBE_INTERFACES’,true)dnl

设为true，sendmai守护进程将不会把本地网络接口插入到已知等效地址列表中。

define(`PROCMAIL_MAILER_PATH’,`/usr/bin/procmail’)dnl

设置分发接收邮件的程序（默认是procmail）。

define(`ALIAS_FILE’, `/etc/aliases’)dnl

设置分发接收邮件的邮件别名数据库。

dnl define(`STATUS_FILE’, `/etc/mail/statistics’)dnl

设置分发接收邮件的邮件统计文件的位置。

define(`UUCP_MAILER_MAX’, `2000000′)dnl

设置UUCP邮件程序接收的最大信息（以字节计）

define(`confUSERDB_SPEC’, `/etc/mail/userdb.db’)dnl

设置用户数据库（在该数据库中可替换特定用户的默认邮件服务器）的位置。

define(`confPRIVACY_FLAGS’, `authwarnings,novrfy,noexpn,restrictqrun’)dnl

强制sendmail使用某种邮件协议，例如，authwarnings表明使用X- Authentication-Warning 标题，并记录在日志文件中；novrfy和noexpn设置防止请求相应的服务，restrictqrun选项禁止sendmail使用－q选项。

define(`confAUTH_OPTIONS’, `A’)dnl

设置由于SMTP验证。

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 使用明文登入。

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 #

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

允许sendmail使用明文口令以外的其他验证机制。

dnl #

dnl # Rudimentary information on creating certificates for sendmail TLS:

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’)

以上四行启用证书。

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

如果密钥文件需要被除sendmail外的其他应用程序读取，那么显示以上行。

dnl #

dnl define(`confTO_QUEUEWARN’, `4h’)dnl

设置邮件发送被延期多久之后向发送人发送通知消息，默认为4小时。

dnl define(`confTO_QUEUERETURN’, `5d’)dnl

设置多长时间返回一个无法发送消息。

dnl define(`confQUEUE_LA’, `12′)dnl

dnl define(`confREFUSE_LA’, `18′)dnl

以上二行分别设置排队或拒绝的接收邮件的系统负载平均水平。

define(`confTO_IDENT’, `0′)dnl

设置等待接收IDENT查询响应的超时值（默认为0，永不超时）

FEATURE宏用于设置一些特殊的sendmail特性。

dnl FEATURE(delay_checks)dnl

FEATURE(`no_default_msa’,`dnl’)dnl

FEATURE(`smrsh’,`/usr/sbin/smrsh’)dnl

Smrsh定义/usr/sbin/smrsh 作为sendmail用来接受命令的简单shell。

FEATURE(`mailertable’,`hash -o /etc/mail/mailertable.db’)dnl

设置mailertable数据库位置

FEATURE(`virtusertable’,`hash -o /etc/mail/virtusertable.db’)dnl

设置`virtusertable数据库位置

FEATURE(redirect)dnl

允许拒绝接收已移走的用户的邮件并提供其新地址。

FEATURE(always_add_domain)dnl

always_add_domain使得在所有发送的邮件上为主机名添加本地域名。

FEATURE(use_cw_file)dnl

表明sendmail使用/etc/mail/local-host-names文件为该邮件服务器提供另外得主机名

FEATURE(use_ct_file)dnl

表明sendmail使用/etc/mail/trusted-users文件提供可信用户名（可信用户可用另一个用户名发送邮件而不会收到警告消息）。

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

设置用于递送本地邮件得命令（procmail）及其选项（$h:hostname，$u:user name）.

FEATURE(`access_db’,`hash -T<TMPF> -o /etc/mail/access.db’)dnl

设置访问数据库得位置，该数据库指出允许哪些主机通过此服务器中继邮件。

FEATURE(`blacklist_recipients’)dnl

启用该服务器为所选用户、主机或地址阻塞接收邮件的功能。（access_db和blacklist_recipients特性对防止垃圾邮件有用）。

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 #

dnl # DAEMON_OPTIONS(`Port=smtp,Addr=127.0.0.1, Name=MTA’)dnl

允许接受本地主机创建的邮件，如果要允许接收从Internet或其他网络接口（如局域网）传入的邮件，一定要注释掉此行。

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 # NOTE: binding both IPv4 and IPv6 daemon to the same port requires

dnl # a kernel patch

dnl #

dnl DAEMON_OPTIONS(`port=smtp,Addr=::1, Name=MTA-v6, Family=inet6′)dnl

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 24×7 DNS do need this.

dnl #

FEATURE(`accept_unresolvable_domains’)dnl

启用accept_unresolvable_domains，使得能够接收域名不可解析的主机发送来的邮件。如果有需要使用邮件服务器的客户机（如拨号计算机），启用该选项。关闭该选项有助于防止垃圾邮件。

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

使域名`localhost.localdomain作为本地计算机名被接受。

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