This is a linux command line reference for common operations.
Examples marked with • are valid/safe to paste without modification into a terminal, so
you may want to keep a terminal window open while reading this so you can cut & paste.
All these commands have been tested both on Fedora and Ubuntu.

I wrote this for myself. Since I have no memory, I write everything down. If it helps you -- great. if you run into problems GTS.  I have no answers. 

I have postfix mapped to a mysql database with three tables: domain, user, alias.

the complete postfix tutorial is here blogging dragon

What he doesn't address, the complexities of forwarding to Gmail,  I will below. Gmail is merciless. If your server isn't getting a 8 or greater at mail-tester.com your email will never see an inbox. 

we are assuming you have crossed that hurdle. 

The grep command searches the given input FILEs for lines containing a match or a text string.

grep command syntax

The syntax is:

grep -options "text string to search” directory-path

OR

grep [option] "text string to search” directory-path

OR

grep -r "text string to search” directory-path

OR

grep -r -H "text string to search” directory-path

OR

egrep -R "word-1|word-2” directory-path

OR

egrep -w -R "word-1|word-2” directory-path