Save the project under a different name, then go into Play mode. Then go to the Play menu, select Playback Template, select Silence and hit OK. Then re-save, compress and upload - it will likely have significantly shrunk!
Go to play and change the Playback Template to Silent and see if that makes the file small enough (in its zipped form) to send.
You can do this to a copy of the file if you have a playback configuration that would be hard to reset.
[You are too fast for me, Leo!]
Removing the cover page took the size to 1.2mb. Using the Silence template did nothing to the file size. Let’s see if it goes through!
As I suggested, your Master Pages are set to filter only the first flow. Untick the box for Flow 1, the filter will reset to “All” and those flows will appear in the score.
Off the top of my head I can’t imagine how you did this by accident, but judging from the number of individual pages that have overrides (44 out of 47) you’ve definitely been fiddling 
I fiddled with frame breaks, that’s for sure. But perhaps I misunderstood you before. Thanks for your heroic efforts on my devil file.
Any time. You can go back and Edit your previous post to remove the attachment, if you’re worried about somebody running off with your string quartet
Well, what do you know. I clicked on all the flows you show above. No change in appearance. They still don’t show up. I give up. I’ll just leave my various sections in separate documents. This is too hard.
Frame breaks don’t cause page overrides. I haven’t checked out the file yet, but it was something else.
Overrides are not a bad thing, but rarely do they need to be applied on the majority of the pages. There may be a better way to achieve what you wanted.
Sent you a PM.
Yes, Dan, it’s true… in old programs like QuarkXpress (and current ones, I expect, like InDesign), you could pretty easily control data flow just by resizing things. I haven’t found such intuitive behavior in Dorico at all, so I would move one stave and there’d be a huge hole (easily fillable, Dorico simply wouldn’t move the thing into the space). The only thing I could find that would work was a hard frame break. So that was a cascade of overrides. Yeesh.
A. I didn’t say “click on all the flows”. I said “untick the first flow” (or something to that affect).
B. You then have to click Apply, then Close.
I know that this works, because I have movements 2 and 3 of your string quartet in front of me.
Whoops, guess I did it backward. OK then.
Yep that did the trick all right. Engrave. Double click master page. Click Flows. Uncheck all flows. And don’t forget the Apply button! Wow! Easy as a soufflé.
I agree it takes time to learn, but it’s worth it. Remember, the more powerful a program is, the longer it takes to learn. One might similarly compare Wordpad to Microsoft Word. The former is easy, the latter is powerful.
Anyways, I’m glad you got it solved.
Incidentally, your overrides appear to be that you don’t like what’s in the Header (specifically “Quartet for Strings”, which is the name of the project). If what you want in your header is “String Quartet - [movement number]”, then I suggest you go into Project Info, select “Project” from the dropdown at the top, then put “String Quartet” into an unused field (such as Lyricist). Then edit the header on your default master page (you already know how to get there) and replace the existing “{@flowTitle@}” with “{@projectLyricist@} - {@flowNumber@}”. Finally, right-click on any page in the Pages section at the top of the right panel of Engrave mode, and then click Remove All Page Overrides. You’ll be left with a page 1 that needs some tweaking, but the resultant learning curve dealing with the First Master Page will be worth it in the long run.
Yes, you both are right. If I can find the right course of action, I will invest the time since it’s the notation app I use every day.