If this an an eg: IMAP, Exchange Outlook, Hotmail, Live type account, could be you don’t have Airsync enabled in your account setup.
Go to “Menu / Accounts” (Pc) or “eM Client / Accounts” (Mac) and select your account. Then click the “General tab” along the top. Then in “Services” part way down see if you have ticked the box marked AirSync…If you haven’t, check that box and then save accounts.