apple mail not sending or receiving

Hi there, I'm using a MacBook Air and despite changing nothing, my apple mail has started to play up this evening. I have always had my iCloud email go through alongside my outlook email. Both have worked successfully along side each other on all my computers including this one. However tonight, it just stopped sending. I get the notification sound to suggest an email has sent, but it never arrives or shows in my sent folder. This is the same for both accounts.

Anyone else having this issue please?