The send is the easy part
Building a campaign is a bounded task with a clear end. Handling what comes back is open-ended, which is exactly why it gets neglected. The work that decides the result has no obvious stopping point.
Group by situation, not by channel
It does not matter whether someone replied by email or WhatsApp. What matters is whether they are interested, have a question, or have already acted. Group responses that way and the next step writes itself.
Make the backlog visible
A response nobody can see is a response nobody will handle. Keep it on screen until someone closes it.