When someone sends an email that you don't have time to respond to (or act on), most of us tend to follow up later, when we do have time. However, a quick acknowledgement will often work better.
Photo by Sebastien Wiertz
Elizabeth Grace Saunders at 99u says this is the perfect time to set expectations, rather than waiting until when you reply:
If you find yourself in the situation where your inbox messages and stress levels are constantly on the rise, you can use these email scripts to reply back and stake a claim over your time by setting expectations from the jump. In many cases, complex projects are a chain reaction of tasks. Most colleagues would much rather get realistic assessments of deliverable times then be ignored or receive stuff late.
That means, even if you don't have time to reply right now, you're better off replying something like "Thank you for your note. I'll be in touch with a full response soon" or "Thank you for your email. I'll need to think through your proposal and get back to you with a decision." You may not have furthered the conversation, but at least they know what to expect.
Saunders has a big list of canned responses for different situations, so I highly recommend checking out the full post at the link below.