EMAILS ARE NOT SENDING

Is anyone else having issues with emails not sending, it is intermittent but some invoices are going through straight away and others are not sending when trying to do so, I either leave it for sometime and it never sends, or I resend them and the customer gets 3-5 emails over the next 60 mins. This has been happening for the last week at least. 

This should be a much quicker action which occurs promptly. Today I have sent 5 invoices, 3 went through instantly, the other 2 I have now sent 3x and still not showing as sent on the invoice activity or my copy has not shown up in my inbox. It is very hard to keep on top of this and it is making my job take longer and making payments take longer to receive. 

THIS IS NOT WHAT I AM PAYING FOR!!