Maybe someone is more knowledgable but I think the biggest issue here is deliverability.
You'll probably have to use a reputable provider's API (eg. GMail, Twilio etc.) because otherwise the recipients' provider are likely to flag you as spam and people never see your email.
You'll probably have to use a reputable provider's API (eg. GMail, Twilio etc.) because otherwise the recipients' provider are likely to flag you as spam and people never see your email.