"Export Photos" in Mail not working

Check in the All Photos view of the library at the bottom. My icon doesn't bounce but the photos end up at the bottom of the All Photos window (the last to be imported) and in the Photos window at the date they were taken. They will not show up in the Last Import album.

I have had the same problem for months now. I have Sierra 10.12.1 on an iMac. The export to Photos function has indeed stopped working - I've been having problems for many months. I've tried having Photos open and closed - the function does not work in either case. I've had to export the photos as files and then separately import them, which is a pain. I believe it started with one of the Photos or Mail updates - but I don't use the function routinely so can not nail down exactly when or why it stopped.

Did you look at the bottom of the All Photos window to see if they were there? They won't be in the Last Import album.

Yes I did look everywhere you suggested. They aren't in the Last Import album, nor All Photos, nor the Photos window at the date they were taken. Your's was a worthwhile suggestion, but it doesn't explain my situation. I've tried a variety of situations such as having Photos open before "exporting", having it closed while exporting then opening it, etc. I've tried every variant I can think of and there is simply no export occurring. I used to do this successfully from Mail (to iPhotos), but the last few months with Photos it is not been working.

As a test launch Photos with the Option key held down and create a new, test library. Import some photos and test to see if the same problem persists. Does it?

The problem persists. Exactly the same result (no import).

Playing around with this further, I solved the problem. I had a couple of iPhoto libraries that were legacies of the replacement of iPhoto by Photos - I had not wanted to delete them until I was comfortable with Photos and knew that all my pictures had been transitioned properly. In Photos, I went to preferences, and selected the Photos library as "Use as System Photo Library". Then I tried exporting from the Mail app, and the pictures properly appeared in the Photos library. I'm not sure where they were going previously (perhaps one of the legacy libraries). I had been unaware that it was necessary to set this preference at all.

Thanks for your help on this issue.