错误详情：
# m4 /etc/mail/sendmail.mc > /etc/mail/sendmail.cf *** ERROR: FEATURE() should be before MAILER() *** MAILER(`local‘) must appear after FEATURE(`always_add_domain‘)*** ERROR: FEATURE() should be before MAILER() *** MAILER(`local‘) must appear after FEATURE(`allmasquerade‘)*** ERROR: FEATURE() should be before MAILER()
解决办法：
按照提示，编辑 /etc/mail/sendmail.mc 文件，将 FEATURE() 放到 MAILER() 之前：
更改
dnl # dnl # Default Mailer setup MAILER_DEFINITIONS MAILER(`local‘)dnl MAILER(`smtp‘)dnl dnl # Masquerading options FEATURE(`always_add_domain‘)dnl MASQUERADE_AS(`tumblr.3sd.me‘)dnl FEATURE(`allmasquerade‘)dnl FEATURE(`masquerade_envelope‘)dnl
为
dnl # dnl # Masquerading options FEATURE(`always_add_domain‘)dnl MASQUERADE_AS(`tumblr.3sd.me‘)dnl FEATURE(`allmasquerade‘)dnl FEATURE(`masquerade_envelope‘)dnl dnl # Default Mailer setup MAILER_DEFINITIONS MAILER(`local‘)dnl MAILER(`smtp‘)dnl
摘自：https://mozillazg.com/2013/02/linux-fix-sendmail-configuration-error-feature-should-be-before-mailer.html
[linux]解决 sendmail 错误： FEATURE() should be before MAILER()
原文：https://www.cnblogs.com/aididiao/p/12489341.html