Cannot send mail in Mac OS X 10.8 Mountain Lion

There is an error while sending mail in Mac OS X Mountain Lion 10.8:

send-mail: fatal: chdir /Library/Server/Mail/Data/spool: No such file or directory

To fix just run in terminal:

sudo mkdir -p /Library/Server/Mail/Data/spool

sudo /usr/sbin/postfix set-permissions

sudo /usr/sbin/postfix start

The solution also fixes an error in 10.8 where the fax service has stopped sending emails after the 10.8 upgrade.

Another Postfix Mac OS X issue solution can be found here: Mac OS, MySQL: No such file or directory (trying to connect via unix:///var/mysql/mysql.sock)