If the software inadvertantly misdirects messages, then the result is unsolicited, so you may want to include an "unsubscribe" link in each response, to protect your sender, and derivatively, yourself, in case the software has an unknown bug.
Also, you may want to ensure that your proposed use is within that of the terms of service for the website, so that you are not in breach of contract with the service (you've probably already thought of this, but I figure I'll mention it).
I could get really ultra paranoid here and suggest that you could be sued for all manner of common law torts depending upon the sender's intent and use of the software and the injury to the recipient. But, that's why businesses puchase general liability insurance -- to broadly protect against what cannot be easily contemplated in advance. You can offset some of this liability by creating an LLC and assigning your product to that entity. Then, if you're sued, only the LLC can lose money. So, that's an possibly cost-effective option to insurance.
Or, you can just "go for it." The choice is yours.
Hope this helps.
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