Recently I am reading Mastering the American Accent by Lisa Mojsin. Here are some quotes from this book:
The vowel within the unstressed syllable is reduced and becomes a neutral, short vowel called the “schwa” and is pronounced as /ə/.
According to it, it seems that all unstressed vowels can be pronounced as schwa.
There are many examples in this book. For instance, the letter e in enjoy is unstressed, so it is /ə/. But in fact, enjoy in many dictionaries is pronounced as /ɪnˈdʒɔɪ/.
Please help me to figure out the correctness of the line above. Is it okay always to pronunce unstressed vowels as schwa?