PowerDNS/pdns — pull request #1672 by petteyg (2014-08-17 18:07:22+00:00)
Title: VARCHAR(255) is too long

Per §3.1:

Domains are up to 255 octets, composed of labels.
Labels are up to 63 octets, including a preceding length octet.
The label for the root is null, i.e. a zero byte for zero length.

With the initial label in the domain taking one octet for length, and the final root label taking another octet, a domain may contain at most only 253 octets.