imap_ssl.search one letter name

Question

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

I want to search emails from a specific one letter named user, "a".
Example:
<[e-mail]>
<[e-mail]>

Problem is, search results cause all users with an "a" as part of there name to be returned.
Example:
[e-mail]
[e-mail]

Any way to isolate the search to one letter name?