No reply is necessary, of course... but... have they received the carefully crafted message at all? Probably. But maybe not?
Do Let People Know Their Mail Has Been Received
Sometimes, emails get lost or fall prey to overeager spam filtering.
- If it is not obvious to the sender that you have gotten their message (because you move forward a project in which they are also involved, for example),
- do send a quick note back, possibly involving an informal thank-you, to acknowledge receipt even if no reply is necessary otherwise.
Even if you do plan to reply later, an email acknowledging receipt and letting the sender know when you will get back to them can be welcome.