sharing email accounts among multiple clients I have configured the default MIUI8 email client with two accounts (one imap and one pop), but I'd like to try other clients. When I install, for example, aqua-mail or k9-mail they ask to configure new mail accounts instead of using the existent, system-level, ones: Settings->Sync->IMAP/POP3.

Is it possible to use multiple clients with the same configured mail accounts?
Yes, it is possible. 

If you use POP3 make sure that you deactivate in all clients deleting the messages on the server after fetching them. Otherwise other clients won't be able to download them. 

Update: to use an already configured system-level mail account, an email app should have an access to system accounts. Not every email app has it.