Well it depends on the label 90%. If they didnt specify any 'preferences', try to send a private SoundCloud link with some info about yourself and why you're sending those tracks to them.
The more personal the e-mail is, the more likely to be replied/considered. No one wants to sign a track/EP which was already listened/downloaded by who knows how many labels/people already.
You're not asking, but I would suggest also to wait until 2 weeks (depending on the label size) to get a response before you send it to another one.
Good luck!