I will try to respond to email messages for which a reply is expected as soon as possible, but on the next working day at latest. During vacation, travel, or in other unusual circumstances the response time may be longer.
However, I receive lots of email and unfortunately sometimes messages are buried and consequently forgotten in my email box. If you are expecting a reply from me and don't receive it within two working days then please re-send your message - I may have lost your email, sorry.
For the same reason please don't trust without confirmation that I will act upon your email.
PS. The information overload has been one of my research topics. We have tried to address the problem with proactive information retrieval. Doesn't yet work with my email box, though...