FIG. 4 is a flow diagram that illustrates an example process 400 for adding users to the user list (e.g., user action group) based on one or more signals. Adding users to the user list can include post-processing and/or selection of users who should receive particular digital components. Adding users to the user list can also include ranking the users in the user list based on one or more contextual signals. The rankings can then be used to identify which users should receive one or more relevant digital components. In other words, the process 400 can be performed to refine an expanded user list to select which users in the expanded user list to send relevant digital components. Operations of the process 400 can be implemented, for example, by the user list generation server 130. One or more operations of the process 400 can also be performed by other components described herein, such as the user grouping engine 114 and/or the content platforms 150. Operations of the process 400 can also be implemented as instructions stored on one or more computer readable media which may be non-transitory, and execution of the instructions by one or more data processing apparatus can cause the one or more data processing apparatus to perform the operations of the process 400.

Referring to the process 400, the user list generation server receives the user list in 402. The user list can be the user list that is returned in 310 in the process 300 (e.g., refer to FIG. 3). For example, the user list can be an expanded user action group that includes users having similar interests as well as one or more users from an original user list (e.g., a user interest group).