I've got OE5 but a quick bit of experimenting has shown me how to lose and then replace the 'Send/Recv' button. Try this:
Go to View > Layout. Check to see if there's a tick alongside 'Toolbar'. (I suspect that there won't be). Click to enter the tick. Click 'Apply' and 'OK'.
If there's already a tick in place, there might be an error with OE. Sometimes removing it and putting it back will work. So click to remove the tick. Click 'Apply' then 'OK'. Then go through the procedure again, to replace the tick.
Chris