[exim] Disabling sender verification for a single host

Hello,

I tried disabling sender verification for one single IP address, but it doesn't
work as expected:

require   verify    = sender
          hosts     = 127.0.1.3

will reject all other mails, while adding an exclamation mark in front of the IP
will reject the mails from this particular IP. What am I missing?

Best regards,

Moritz