Q: Unsent message in my outbox

Hey thanks for the reply. 

I'm using my Macbook Pro Mac Mail. 

Mail providers are google mail, icloud.com and also 123-reg mail (numerous email accounts)

I'm sending/receiving OK on my Iphone.  Looks like I'm not sending or receiving on my Mac either now.  Outbox mail has been piling up since yesterday evening.  Connection Doctor is green on all accounts. 

I've tried all this and it doesn't help with my issue. 

I have received emails on my Mac which are being emailed from other IP addresses, but cannot send or receive my own. 

Actually, I forced closed all items and on restarting my machine, it all works well. 

Many thanks in any case.