dstiles - 6:36 pm on Apr 27, 2013 (gmt 0)
keyplr - I have the usual set of G IPs, all of which are blocked except those assigned crawler status in DNS and a very small range of utilities. This range was a new range, set up in DNS late-ish last year. I can post a full list of what I have if required.
kendo - you are confusing web and other internet services. Mail, FTP, SSH etc should never access web sites on ports 80 or 443. Apart from which, they run on different servers (although often on the same computer); I run mail, FTP and web servers on a single computer and each service has a different server and associated ports. Mail servers run on such ports as 25, 587, 110 and will never send get or post requests to web servers. Hence they can be blocked as unwanted. If any mail service tries to access our web sites they are doing so "illegally". Those of us running web forms or webmail make our own inter-service arrangements.
As we've said, there are only a few bots we allow or should allow.
As to "IT professionals" using their own mail servers - in some cases that is valid, providing the server is hosted on a proper server with a fixed IP and proper DNS setup. I do that for myself and my clients. I've seen (and blocked) a fair few idiots trying to send mail from their "home" or "office" computer, often on a dynamic broadband line. They invariably claim to be "professionals" and that their mail is not rejected by other mail services. It's always fun when they turn off the computer each night.
People who run internet services of any kind need to know at least how to run their own services and preferably know a reasonable amount about services they do not operate.