I think so. You can make a contract via e-mails. When you purchase something on the internet you are effectively making a contract using electronic data.
If you're making an offer and the other party accepts those terms via reply, then yes it could well be. But it would always be prudent to follow up with a formal contract.
Yes it can be binding. There are still some transactions that can't be done electronically like land transfers etc but for general day to day business, an e-mail is an accepted form of contract. An e-mail coming from my account with my name is usually enough to be considered an electonic signature. There is Irish and European Law on the subject.