The internet is so messed up that I have to send many posts at least twice, and sometimes three or four times.
When I have finished writing a reply, I copy my post quickly and easily. Hold down Ctrl, touch A, let A go, then touch C. It highlights then copies everything and when the post doesn't go through, you can re-open the window and put your mouse cursor in the white field, and press Ctrl-V (both keys at once), and there's your post again. Hit "Send Message" again and repeat as necessary. But the Ctrl-A-C is necessary only once. Don't make a second post until the first one goes through and then you can make and copy the second, etc. Takes a small moment and keeps you from losing the post you have written.