Jetpack email subscription

I would love to know the reason why of my 173 email subscribers only 1 is an identifiable person! Is it some sort of spammers paradise generated by Jetpack?Here is a selection:-

groovyardor670ki38 @outlook.com 6 days, 6 hours ago
gorgeousvalley35mj37@laposte.net 6 days, 8 hours ago
skillfulcrook41kv651@outlook.com 6 days, 9 hours ago
calvocyt@hotmail.com

The last twoe appears on spamlists like here http://cleantalk.org/blacklists/calvocyt@hotmail.com So it looks like it’s best to avoid Jetpac’s Email signup option!

Anyway I’ve deleted it now although there doesn’t seem any way of clearing the existing people.