Can't exchange emails between two eM Client based email accounts

I’ve just installed the free version of eM Client on two different PC’s. Each PC has one unique email account. I can send/receive emails without difficulty to/from all the parties in my address book, but I can’t send/receive emails to/from the eM Client based email account on the other PC. An email will appears in the Sent folder of the sending PC but never appears in the Inbox of the other PC.