First of all, you must enable the SharePoint library or list to accept messages from any sender.
To verify whether you have the correct settings, go to the library or list and click Settings > Document Library/List Settings. Under Communications, click Incoming Email Settings.
Incoming email settings should look like this:
You cannot receive messages to the SharePoint list or library from external senders because our servers are not configured to accept emails from external servers due to security reasons. However, you may use the following workaround.
To configure mail delivery to the SharePoint list or library from external email addresses:
- Create a contact for this SharePoint document library in CONTROL PANEL, on the Services > Company Contacts page. The contact should have the same email address as a mail-enabled library or list. In the above example, the contact would have firstname.lastname@example.org for the email address and any Display Name.
- Create a distribution list in CONTROL PANEL, on the Services > Distribution Lists page. The distribution list should have the email address that you will provide to your customers to send documents to.
- Make the created contact a member of this distribution list.
Example: the distribution list email address is email@example.com. The Company contact firstname.lastname@example.org is the only member of this distribution list. To send messages to the document library, external users will send to email@example.com. The message will be forwarded to firstname.lastname@example.org and then appear in the document library.
When you have set this up, mail sent to this distribution list should be delivered to your SharePoint site.