Sendmail/Postfix Info

Sendmail view mailq:
mailq
sendmail -bp

Sendmail view verbose info:
sendmail -v

Postfix flush mail queue:
sudo postfix flush
sudo postfix -f

Remove all mail in queue: 
sudo postsuper -d ALL

Remove all mail in deferred queue: 
sudo postsuper -d ALL deferred

Postfix Info
http://www.akadia.com/services/postfix_mta.html

http://www.cyberciti.biz/tips/howto-postfix-flush-mail-queue.html
http://www.unix.com.ua/orelly/networking/tcpip/ch10_08.htm
http://shinphp.blogspot.com/2011/09/ubuntu-clean-sendmail-queue.html

Join UNIX Command

Join takes two sorted text files and joins them together on common keys, similar to the Join SQL statements.

Basic join syntax:
join file1 file2

Specify a delimiter other than the default of whitespace (for input and output):
join -t: file1 file2 # sets the delimiter to be a colon


Join on specific columns in each file:
join -1 1 -2 1 file1 file2 # this will make file1's first column join with the file2's first column.

Join on a specific column and output specific columns:
join -11 -21 -o 1.1 1.2 2.1 2.2 file1 file2 # the -o options takes space-seperated arguments that take the form of file.column to specify only particular columns.

Specify filler text in a result column when two keys do not match between files:
join -e "none" file1 file2 -o 1.1 1.2 2.1 2.2 # the -e option needs to be used with -o

http://www.softpanorama.org/Tools/join.shtml
http://www.computerhope.com/unix/ujoin.htm