Email Field Being Dropped on sendMessage (Craft Contact Form Plugin)
If you go with the message[] array syntax, then all other fields must use the same syntax.

https://github.com/craftcms/contact-form#adding-additional-fields

So this should solve it:

&lt;input id="fromEmail" type="email" name="message[fromEmail]" value="{% if message is defined %}{{ message.messageFields['fromEmail'] }}{% endif %}" required&gt;