如果使用的是邮件协议，那么将域标记为垃圾邮件的可能性更高吗？ * nix，机会是mail（）和sendmail（）相同。 mail（）仍将使用sendmail，但它将传递您在php.ini中定义的所有参数。

If you're using *nix, chances are mail() and sendmail() are identical. mail() will still use sendmail, but it passes any arguments you have defined in your php.ini.

SMTP和sendmail之间的区别更大。如果您要进行大量电子邮件发送，则要使用SMTP，因为sendmail会为每个电子邮件打开一个新连接，这会增加很多开销。

The bigger difference is between SMTP and sendmail. If you are doing a lot of mass emailing you want to use SMTP because sendmail opens a new connection for each email which adds quite a bit of overhead.