In Sharepoint you may configure Access request settings which will allow users to ask for access to the site from appropriate responsible person (I intentially don’t tell site owner here because recipient of access requests may be different person – see below). In order to do it first of all you need to configure outgoing email settings in Central administration. Access request settings for web site may be configured from Site settings > Site permissions > Access request settings:
When you click this link Sharepoint loads setrqacc.aspx into modal window. If we will check its codebehind class Microsoft.SharePoint.ApplicationPages.SetRequestAccess we will see that it first checks SPWebApplication.RequestAccessEnabled internal property:
In this property it checks another property IsEmailServerSet:
which in turn checks outgoing email server address:
That’s why setting outgoing email settings should be done before to configure Access request settings.
Now let’s check SetRequestAccess.OnLoad method again and see how “Allow access requests” checkbox is initialized with checked/unckecked values. As it is shown above OnLoad method calls ToggleSelectedAndSetObjectType method:
and the last one checks “Allow access requests” checkbox when SPWeb.RequestAccessEnabled property set to true. Let’s check code of SPWeb.RequestAccessEnabled property:
I.e. it is readonly property which returns true only when Access request email is set, i.e. other property SPWeb.RequestAccessEmail. So basically in order to enable Access requests you need to set SPWeb.RequestAccessEmail for your web site.
The problem however is that Sharepoint for some sites sets SPWeb.RequestAccessEmail to default value email@example.com – see first picture in this post. There is internal method SPWeb.EnableAccessRequestsIfNeeded where it is done:
Here it’s code as it doesn’t fit to post column’s width:
So for root webs of new site collections which have HasUniqueRoleAssignments = true and which use web template id except 3, 16, 17, 18 (and of course if SPWebApplication.RequestAccessEnabled is set to true – see above) Sharepoint will set SPWeb.RequestAccessEmail to default value firstname.lastname@example.org which will mean that Access requests will be enabled there by default. In the following forum post Access Requests recipient by Default it is mentioned that in this case, i.e. when default email address email@example.com is used, SPWeb.Site.Owner.Email will be used for sending access requests, although I didn’t check it by myself.
And one more thing: if you are working with CSOM note that Web.RequestAccessEmail property is available there only starting with version 16.1.4727.1200 onwards. Basically it means that it is not possible to change Access requests settings by CSOM for Sharepoint 2013 on-premise. It is still possible though via basic server object model.