A 5 MB bitmap (bmp) attachment can be problematic on the outlook side depending on several factors, , but I would not bet on that as the root cause. It might be a bmp issue, but my guess is that's also not it; Aware would need to confirm. I can recommend a few troubleshooting steps though...
- Try a smaller .bmp like 1px by 1x - this can be created with MS Paint on any windows PC
- Get Fidler web debugger (freeware). Turn it on and run the query, then see if the the query returns and if so what is being returned specifically. This will not fix the issue but can tell you where the trouble is
If those both look ok, then maybe checkout these ...
- Verify that the BMP is an attachment or if it is embedded (I don't think it's this but worth a look)
- Verify the client has a .bmp viewer
- check that the server has the right MIME type for a .bmp