My computer background info:
Windows XP SP2. Using Comodo Internet Security Premium (5.9.221665.2197) Virus def: 11477. A few months ago, installed the Comodo Dragon browser out of curiosity.
The morning of February 9, 2012 using FireFox, I could log into hotmail.com to read and send email. And, could visit other websites without issue. However, in the evening using FireFox, could not access the login page for hotmail.com. I got an error message about the server (error 108; unfortunately, I did not write the error message down). But, otherwise, I could visit cnn.com, globeandmail.com etc. I tested other email websites, like bell.net, gmail or yahoo mail. I got the same error message. The problems could be duplicated in IE and Comodo Dragon. Most interesting, visiting non-email sites presented no problem at all for all three browsers.
Poked around using Google (as well as the Comodo forum) and could not find a suitable solution. Disable CIS Premium, no effect. Flushed the DNS, no effect, rebooted, no effect. I then slept on the problem and reasoned that the problem was common to three different browsers and was independent of CIS premium. Now, what else was common to the three browsers? Answer: the DNS settings on my computer.
In the morning, I checked the DNS setting (I knew they had been changed as part of the Comodo Dragon install a few months ago). The DNS settings were now 22.214.171.124 and 126.96.36.199 --- both of these are Comodo settings … changed the second one to 188.8.131.52 … the problem of just visiting the login pages for hotmail, gmail and yahoo mail still persisted. However, when I changed the DNS setting back to what I had before, that is, 184.108.40.206 and 220.127.116.11 and I could visit the login pages for and log into hotmail.com, bell.net, gmail and yahoo mail. The problem was resolved by not using the Comodo DNS Servers.
I hope that this solution can help others with similar problems.
Any explanation as to why the Comodo DNS servers would work in the morning but not 10 hours later (with the problem still persisting 12 hours later)?
AN ASIDE: This reminds me of a problem that I had about 5 or 6 years ago with Bell Canada and surfing. Some websites would just disappear and reappear within minutes. Even within a single browsing session of less than a minute, I could read a page and click on a link to another page on the same website and get an error message that the domain does not exist. Bell Tech support was no help. I eventually found the idea to change the DNS settings to 18.104.22.168 and 22.214.171.124 and my problems went away. I know nothing about inner workings of DNS servers .. this is my experience with DNS. Solution: keep a listing of DNS servers and know how to change the DNS settings on your computer.