Command grep for extracting email addresses from big text files. You can pass it multiple files. Tested on large 190GB file (with 152,353,216 lines)

gistfile1.txt

# split the file into a file of 50,000 lines.
split -b 50000 bigfile.txt

# OR split the file into a 100MB file.
split -b 100M bigfile.txt

# extract the email addresses contained in all the files of a directory
grep -r -E -h -o "[[:alnum:]+\.\_\-]*@[[:alnum:]+\.\_\-]*" /dir/* > emails.txt

# remove duplicates and sort order ASC
sort -fu emails.txt > unique_emails.txt

UPDATE

The simplest (but probably not the quickest) way to process all the files would be to do so one by one, using a loop:

    for file in /dir/*; do
      grep -r -E -h -o '\b(pattern)\b' "$file"
    done > outs.txt
The overhead of launching all those `grep`s is potentially quite significant, though, so maybe you could use `xargs` to help:

    find /dir/ -maxdepth 1 -type f -print0 |
      xargs -0 -n 1000 grep -r -E -h -o '\b(pattern)\b' > outs.txt
This uses `find` to produce the list of files in `dir` and passes them safely to `xargs`, separated by a null byte `\0` (a character guaranteed not to be in a filename). `xargs` then passes the files to `grep` in batches of 1000.

(I'm assuming that you have GNU versions of `find` and `xargs` here, for `find -print0` and `xargs -0`)


EX. 
find /dir/ -maxdepth 1 -type f -print0 | xargs -0 -n 1 grep -r -E -h -o '[[:alnum:]+\.\_\-]*@[[:alnum:]+\.\_\-]*' > emails.txt