grep -E -o "\b[a-zA-Z0-9.-]+@[a-zA-Z0-9.-]+.[a-zA-Z0-9.-]+\b" filename.txt
You can also use egrep instead of grep with the -E switch.
egrep -o "\b[a-zA-Z0-9.-]+@[a-zA-Z0-9.-]+.[a-zA-Z0-9.-]+\b" filename.txt
grep -E -o "\b[a-zA-Z0-9.-]+@[a-zA-Z0-9.-]+.[a-zA-Z0-9.-]+\b" filename.txt
You can also use egrep instead of grep with the -E switch.
egrep -o "\b[a-zA-Z0-9.-]+@[a-zA-Z0-9.-]+.[a-zA-Z0-9.-]+\b" filename.txt