v1 <- c("I will try to fix you usman@usman.com", "I will try to fix you", "Zombies Zombies xyz@ymail.com")
v2 < c("ABC", "XYZ", "Oh Game")
dx <- data.frame(v1, v2)

ABC       usman@usman.com
XYZ       NA
Oh Game   xyz@ymail.com

dx$emails <- sapply(dx$v1, function(x) {
  email <- regmatches(x, regexpr("[[:alnum:]]+\@[[:alpha:]]+\.com", x))
  (result <- ifelse(identical(email, character(0)), NA, email))
})