I have problems with deliery errors. This is the second month in a row. After clinking send several times it does go. but not ideal. Anyone has a solution?

It is not new email address and there is not just from one company and I have already checked it is nothing there end. I can email them fine. 
I spoke to someone at QB last month that said they have done some updates and that it can take some time for my browser to getin lign with that and should sort itself out. An in the end all invoics got sent. But I had to lick send 10+ times. It just came bouncing back until it finally disappered.