You can get it back quickly in just a few mouse clicks. Go to View -> Customize Toolbar. The pop-up has two panels. The one on the right has buttons that are already present in the toolbar while the left panel contains those that can be added to it. Spot "Send/receive" in the left panel and put it back on the toolbar by clicking on the button that has an arrowhead pointing to the right. Click on the "OK" button and you are done.
If you are using Windows Live Hotmail then that is not the same as Windows Live Mail.
And are you referring to the Sent folder (which shows messages you have sent) or to a Send button. If the former then I suggest you might have collapsed the folder headings - to expand just click on the word Folders (just under Inbox) and they will return.
Or do you mean something else?
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