Wrong regex for extracting From domain

[marc-vanderwal]

The following line uses a regular expression to attempt extracting the domain name of the From header:

https://github.com/pimlie/authres_status/blob/eba58333b1b8e3f0028796857719e77a4dfb767d/authres_status.php#L353

However this regular expression is incorrect, for several reasons:

• domain name labels (including top-level domains) may also contain hyphens;
• TLDs exist that are more than 4 characters long, e.g. .paris (and there are much longer TLDs on ICANN’s list).

On a closed test network where I was using domain names ending in .example, this causes an e-mail whose sender domain is sender.example to be labeled STATUS_THIRD by this plugin despite SPF, DKIM and DMARC passing, all at sender.example. Adjusting the {2,4} to {2,7} as a test yielded STATUS_PASS instead.