Subscriber emails not sent

Hi, I’m having trouble with subscriber emails. When I try to send an email to one person or even 100 people everything works fine but when I try to send the email to all my subscribers (~1000) it doesn’t work – I get no ‘mail sent successfully’ and it doesn’t appear in the sent mails tabs, so I don’t know if it was actually sent or not. Do I just need to break it down into smaller groups or is there a way to resolve this? Thanks.