Mail Not Connecting.. For Three Weeks

Question

For the last three weeks Mail hasn't been connecting - I can't send or receive mail at all. It's basically the same problem as this person was having here: http://discussions.apple.com/thread.jspa?messageID=10543385&#10543385
iChat wasn't connecting either, until yesterday when I fiddled with the ports.
Firefox works fine but Mail, WoW, Steam, Transmission, etc. do not connect. I've done a malware scan and nothing turned up. My landlord says he isn't blocking any ports. This started about three weeks ago. One day, everything was working fine.. the next day nothing would connect.
Does anyone know what I could do to get Mail working again? Or what the problem may be?

Answer 1

I was rather hoping you were going to tell me that the PC was able to access email and that this problem is therefore restricted to the Mac. If it wasn't for the fact that you are unable to connect from the library as well I would suggest that it is most likely to be an issue with the router or ISP. I think it is still worth asking your landlord if they will check that the firmware is up to date on the router and if it isn't if they could update it, At least if they check it will eliminate something from the equation.
In the meantime I guess we can check your email ports. Go to https://www.grc.com/x/ne.dll?bh0bkyd2 click on 'Proceed', then 'Lookup Specific Port Information' then enter 995 and click 'Jump' then click 'Probe THIS Port'. Repeat the probe for port 587. You can also ping the GMail server by going to /Applications/Utilities/Network Utility/Ping enter gmail.google.com and click Ping. Obviously I am concentrating on the ports that GMail will use and you can probe other ports used by your other apps that can't access the internet.
Try this, in Terminal (in your Utilities folder) enter
dscacheutil -flushcache
to flush the DNS cache
Still in Terminal enter:
sudo /sbin/ipfw -f flush
... and type in your password when prompted. This will clear out your existing Firewall rules so if you had any set up you will need to recreate them.
You could also go into System Preferences/Network and create a new 'Location' use that and test. It might be useful if you could also test your connection at the library or some other place using this 'test location'.
Report back with what you find and we will see where we can go from here. Hopefully you do find something because the ideas are starting to dry up and unless Golden Shoes or someone else can come up with something we may come to a dead halt here.
BTW are you sure you looked in the right place for the Receipts folder? It should be in /Library where I said, at the top level of your HD not to be confused with the one in your User folder or the one in System