To get number of messages sent by each Marketo user

Unfortunately, don’t think there’s a way to do this.

Only place where the user who scheduled a campaign — a dubious proxy for “owning” a campaign in many organizations anyway— is logged is in the Asset Audit Trail. And that’s only kept for 6 months.

This would be an example where naming conventions are useful. I suppose your users are assigned to various aspects of your business, such as business lines, products or regions. If you are rigid with including these "aspects" in your program names, you can report on these names.

You could even to consider to add your users' names - or their initials - to program names.

But eventually, I don't think this is a really meaningful report. Users come and go, but business lines, products and such stay and it should be more impactful to get answers to questions like "How many emails were sent for product A in region B".

This won't help you now but you could consider creating a program tag for "users" and pull reports that way in the future(assuming that your users are creating their own campaigns in all cases).  I'm not sure I'm really a fan of that approach because people come and go from an organization but it would allow you to at least see who is building what if you really need that level of reporting on a regular basis.  I've seen instances setup this way for that reason. 

That many users is quite a lot to manage 🙂 

@sg-3 please return to your thread and check community responses.