Outgoing mail

I suddenly cannot send mail. This happened once before and it took me having to delete and start over input of each of two email addresses onto each of my MacBook, iPad and iPhone to make them all work again. Now it’s happening again. The error I get says there’s a problem with the recipients address, but it’s everyone, so nope. I really don’t have half a day to redo all the settings. Anyone have a quicker path to fixing this?