Hi, thanks for your feedback. 'MAINSTREET' doesn't seem to be a correct English word, it should be 'Main Street' instead. I suppose that's why it's spelled out. However, you can improve the pronunciation of the word using SSML. Below, I've defined SSML to improve pronunciation using say-as element.
<speak xmlns="http://www.w3.org/2001/10/synthesis" xmlns:mstts="http://www.w3.org/2001/mstts" xmlns:emo="http://www.w3.org/2009/10/emotionml" version="1.0" xml:lang="en-US"><voice name="en-US-JennyNeural"><prosody rate="0%" pitch="0%"><say-as interpret-as="address">MAINSTREET</say-as></prosody></voice></speak>
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--please don't forget to Accept Answer
if the reply is helpful. Thanks.--