Restrict permissions of new members

In large Zulips where anyone can join, it can be useful to restrict what new members can do, to make it easier to cope with spammers and confused users.

Members are new members from when they join till when their account ages past a certain waiting period threshold. After that they are full members. You can configure how long the waiting period is, as well as which actions require being a full member.

Currently, the following actions support limiting access to full members.

• Creating streams
• Adding users to streams

Set waiting period for new members