The delayed joins feature allows channel operators to essentially squelch join/part floods.
How does it work?
Users joining a delay-joined channel are considered "observing," and no join notification is sent. If that user later sends a message to the channel, changes the channel's topic, or a mode change occurs on them (e.g., voiced or opped), they're considered "revealed," and a join notification is sent to your client.
How do I enable delayed joins in my channel?
Any channel operator can enable delayed joins by setting channel mode +D.
For example: /mode #darenet +D
Likewise, unsetting channel mode +D will disable delayed joins.
Note: Disabling delayed joins while there are still delay-joined users (e.g., hidden) in the channel will cause channel mode +d to be set automatically. We'll cover that below.
Why is +d set on my channel, and why can't I remove it?
As mentioned above, the channel mode +d is set automatically whenever the delayed joins feature is disabled, and there are still delay-joined users present in the channel. When all of these users have been revealed or part the channel, the server will automatically remove +d. You cannot remove or set +d on your own, but you can voice those users who were hidden by delayed joins to reveal them.
How do I view delayed-joined (hidden) users in a channel?
You can view users hidden by the delayed joins feature using the /NAMES command with the -D argument.
For example: /names -D #darenet