Workspace Owners and Admins can decide who can set posting permissions for the #general channel:

1. Click your workspace name in the sidebar.
   
2. Hover over Tools & settings, then click Workspace settings.
3. Click the Permissions tab at the top of the page.
4. Scroll down to Channel Management and click Expand.
5. Below People who can manage posting permissions in channels, select an option. 
6. Click Save.

Workspace Owners and Admins can decide who can set posting permissions for any channel:

1. Click your workspace name in the sidebar.
   
2. Hover over Tools & settings, then click Workspace settings.
3. Click the Permissions tab at the top of the page.
4. Scroll down to Channel Management and click Expand.
5. Below People who can manage posting permissions in channels, select an option. 
6. Click Save.

Org level

Org Owners can set an organization policy to specify who can manage posting permissions:

1. Click your organization name in the sidebar.
   
2. Hover over Tools & settings, then click Organization settings.
3. Click  Settings in the left column, then select Organization Policies.
4. Select the Permissions tab.
5. Next to Channel Management Restrictions, click Add Policy. 
6. Under Who can manage posting permissions in channels, select an option from the drop-down menu.
7. Click Save Policy, then Confirm Policy.

Workspace level

Workspace Owners and Admins can decide who can set posting permissions for their workspace:

1. Click your organization name in the sidebar.
   
2. Hover over Tools & settings, then click Workspace settings.
3. Click the Permissions tab at the top of the page.
4. Scroll down to Channel Management and click Expand.
5. Choose who can manage channel posting permissions.
6. Click Save. 

Tip: In default org-wide channels, posting is restricted to owners and admins only.