imap_ssl.search one letter name

Code:

resp_code, mails = imap_ssl.search(None, '(FROM "a")')

I want to search emails from a specific one letter named user, "a".
Example:
<a@xxxxx.com>
<a@xxxxxx.com>


Problem is, search results cause all users with an "a" as part of there name to be returned.
Example:
jane@xxxxx.com
aaron@xxxxxx.com

Any way to isolate the search to one letter name?