This post is about how to add attachments in GMail in Android 2.3.x from the file system.Granted, many people are stuck with Android 2.3.x, so the post is specific to that branch of Android.
GMail appThis happened to me with the GMail app version 2.3.6 in Android 2.3.6 on a lower-end Samsung phone.
A few days ago (that was around 17.05.2015) I was trying to send two crash log files of a different app to its developer via Android's GMail app, and for some reason, sending the e-mail didn't work. I don't quite know why, and I lost the e-mail. One attachment was relatively small, and another was around 860 Kb (a bit large in some respects). I haven't investigated this issue online.
A day later, putting attachments in an e-mail in the Android GMail app and seeing that same letter as a draft in GMail on the web did work:
• If you insert attachments first in the GMail app, then do write some text into the message area, which unblocks the save-as-draft button; save the letter as draft and sync.
I haven't investigated how to do that in a browser in GMail, given that the GMail app method worked out for me.