I tried today to E-Mail receipts using my smartphone running Android 8.
The issue here is that the camera app is directly integrated with Google Photos (which used to not be the case), and therefore sharing from the camera app sends the receipt picture from the domain “google.com”, e.g.
We’ll leave this thread open for others to add their feedback and comments.
In the meantime, you can use an email app on your phone to email it in, or alternatively use a third party service such as Dropbox. Although we don’t currently support Google Drive (there is a separate feature request for this if you want to add your vote), you may be able to set up a Zapier rule to transfer it to somewhere like Dropbox or perhaps even email it (I haven’t tested this).