Is this something that requires your attention right now? If yes, either pick up the phone or stop and shift your focus to responding. Many times that back and forth virtual exchange is caused because one party (sometimes more) is multi-tasking and not fully reading the exchange. If you stop and focus and send back a complete response and then get back a response too quickly, chances are you are dealing with someone who is giving the conversation less than his or her full attention. You can either pick up the phone or hold off on responding hoping they will re-read your message. (You will know because these are the same people who will respond again saying something like "Never mind, I just read your full response.")
TIP: to avoid being that person, do not view your emails in preview mode unless you are searching for a particular email. Preview mode, when used exclusively, generally is a crutch and most people who use it exclusively only respond to what they read in the preview (and likely miss a lot of important information).
If you cannot respond immediately, acknowledge that you cannot but that you have received their message. An automated response system like Outlook's Out of Office Assistant is good if you will be gone or out of pocket for an extended period of time.
TIP: Try closing your e-mail for an hour or two to focus on a project and use your auto-response tool. You can always say if it is an emergency you can be reached via phone.
When you acknowledge that you have received their e-mail, commit to responding within a reasonable amount of time. If you are taking two hours to work on a project, commit to responding in four and make sure you spend the two hours responding as needed. If something requires some research, respond and let the person know that fact and give them an estimate of when they will hear back from you. "Later" does not count.
TIP: Be logical on this and look at your schedule when committing. Give yourself a little extra time for those things you know will pop up.
4. Follow Through
This is the hard one. You commit to things at the beginning of the day or week that seem reasonable and then "emergencies" pop up that require your attention. Try to be reasonable and give yourself some room when committing, but if you absolutely cannot make a commitment, let the person know you haven't forgotten them and when you will respond (and move that to the top of your priority list).
TIP: Use the reminder function in your e-mail to pop the e-mail up before you have committed to respond when you will still have enough time to research.
Of course, anywhere along the way you can delegate the task will help. If you are delegating to someone else, make sure they know when a response is required by and encourage the requestor to reach out to you if they don't hear back.
How do you balance staying plugged-in and focused during the week?