# ... up to this point, 
# you must have read 1 line from the file ...
# and (for sake of example) the email field saved in into $email_field variable.
my @emails;
while ($email_field =~ m/SMTP:([^\%]+)\%/g) {
  # validate matched email first... (as per UPDATE)

  push @emails, $1; # add email address to the list
}
# @emails array now contains all SMTP email addresses
# found in the field.