Extract mail addreses from files or downloaded site

======================================
grep -Eiorh '([[:alnum:]_.]+@[[:alnum:]_]+?\.[[:alpha:].]{2,6})' ./ > emails.txt
======================================

This makes grep find all email addresses and write them to file emails.txt in the current dir.
-E makes grep use extended regular expressions
-i does a case-insensitive match
-o makes grep return only the matching part of the line and not the whole line
-r makes grep look files recursively
-h stops grep from outputting the filename where the match was found

with the r parameter and the source file as ./ grep will go through all the files in the current directory and sub directories. The weird looking string in the line is the regular expression which looks for emails.