For example, when searching with "quest" for content containing word "questions" starting from beginning of word, Gmail returns result:
However if searching with "est", no results are being returned.
Typing in the "To" field autocompletes the contact from the start of a word, not just the start of the contact name or email address. So, if you have a contact called "Joe Bloggs", you can start searching on the
b of "Bloggs" ie:
If, however, you want to do a complete search of your contacts, you can click on the label "To" and this opens all your contacts in a handy popup, complete with a search box. Select all the contacts that you wish to address the email to and click Select.