Is it ok to send a thank you card by email for a birthday party gift?

Opinion

It is your personal choice. However, you should only really consider it if you didn't receive the gift in person. If you did then chances are you would have already verbally thanked the person.

Opinion

Absolutely. A quick thank you at the time you receive the gift does not acknowledge all the effort the gift giver spent in shopping, choosing, wrapping and giving you that gift. It is more important than ever in this world of diminishing personal contact to send a quick thank you note acknowledging the gift and the giver. Many people don't bother with thank you notes but that doesn't make it the right thing to do. A thank you note received by the gift giver will produce as much pleasure as the recipient felt upon receiving the gift. Many people stop sending gifts that are never formally acknowledged.