A new Crawl Error alerts features has been introduced by Google Webmaster Tools. This means the website owners will now be informed of Site Errors for major site-wide problems.

In the past Google only sent alerts about website problems for a subset of serious issues - such as being hacked, needing a software upgrade or having problems with malware or spam. 

Now, webmasters can expect to receive e-mailed alerts with respect to issues that the Googlebot encounters while crawling their sites. Google enhanced its Crawl Errors feature back in March 2012 and since then has organized them into two categories:

• site errors that affect an entire site and represent systemic issues that prevent connecting to a site
• URL errors that are specific to a page such as 404 (Not found) errors

The new alerts are for the former category and might stem from the following causes:

• DNS server is down or misconfigured
• Web server is firewalled off
• Web server is refusing connections from Googlebot
• Web server is overloaded, or down
• Site’s robots.txt is inaccessible

An alert provides the number of errors Googlebot encountered crawling your site, the overall crawl error connection rate for your site, a link to the appropriate section of Webmaster Tools to examine the data more closely, and suggestions as to how to fix the problem.