Why wont my mailbox sync

Mail
1

My email won’t sync, even when I press the refresh button. Does anyone know why?

2

Have you tried this:  Go to “Menu” ‘Tools’ then ‘Accounts’ & run diagnostics. Also enable the Diagnostic logs for IMAP & SMTP

3

I tried but the fixing failed Why?.

4

Under “Menu” “Tools” & ‘Operations’ what errors are being reported?