@HarryCheung has tested mobile app by reimplementing the same app with 13 different languages. This includes C++ (fastest on iOS and Android), Swift, Xamarin, J2ObjC, Javascript & RubyMotion (slowest on iOS). All the code is available on GitHub for the community to improve further. Disclosure: I provided feedback on the posts but was not involved in the testing.

The 0.01% of many skilled professions keeps the world turning and we can be grateful for that. As an engineer in my mid-30s, I believe much more strongly now in pushing for simplification. I know from many bitter experiences that trying to do things outside the norm often invites unintended consequences. As a consequence I try and be very strategic about what complexity I take on to make sure it's worthwhile. For me, I use the web Gmail interface and a gmail address. Not the same as running your own domain but I've found it's worked pretty well for me.

Disclosure: my name is Bruno Bowden and I managed the engineering team on Enterprise Gmail many years ago at Google before leaving to work in venture capital. My profile is www.linkedin.com/in/brunobowden. Though I didn't work on spam fighting directly, I interacted a great deal with the spam team while I worked there.

One of the main architects of the spam fighting system - Brad Taylor - published a scientific paper on "Sender Reputation in a Large Webmail Service" - http://www.ceas.cc/2006/19.pdf. This has a lot of detail about the system. We keep much of the internals secret as it reduces the chance that a spammer can reverse engineer and work around the system. If you'll allow me to be vague, the number of signals it uses was stunning to me. There's a mixture of hard wired tests (e.g. is the sender in someone's address book), reputation (domain and content), machine learning and anything else we can make work.

One of the principle improvements came when we switched to user classification through the "Report Spam" button. People have different opinions on what constitutes spam, so individual filtering is far more effective. It also avoids the politics of certain lists of domains and IPs from third parties which can be controversial. Even then it has challenges, as sometimes users will mistakenly pick out a phishing email and mark it "Report Not Spam". Because of that, Gmail now adds a red warning banner to indicate more strongly what is a likely a phishing attempt. In general, Google has tried to be very supportive of encryption, e.g. DKIM for authentication (and SPF) to STARTTLS for privacy. I would also like to mention the abuse team that works hard to prevent gmail being used as a source of spam, shutting down accounts as soon as possible after suspicious email is sent, then helping affected users to recover their account.

In general, the Gmail has received a lot of compliments on the spam filtering, I'm sure the team will be grateful for the positive comments here on Slashdot. There are still things that can confuse the system, e.g. receiving forwarded email (which might be missing source IPs) or genuine email that is sent to the wrong address. Though the system isn't perfect, I know the team will continue to work hard on it.