My gmail or icloud mailbox has no incoming mail, showing that the mailboxes are connected but nothing coming in, mailbox rebuild option is greyed out. any ideas?

My mail has suddenly stopped receiving any incoming mail, I have gmail and of course icloud but nothing coming in or going out. I've ran the connection doctor and it's showing that the connection to the internet is fine, so where is the mail?

Cannot rebuild mailbox as the option is greyed out...any ideas?

I can access my gmail via the internet so posts will be seen.

thanks, any advice will be welcome as i'm at a loss.