I know this is a tad old, but future searchers may still run into this.
I had this issue, and here's what my problem was.
I use Trend PC-cilling Internet Security, and my personal firewall settings had about 30 entries for MS Outlook as an outbound exception.
They all had the same exact settings.
I deleted all but one of those firewall exceptions, doubled checked the remaining one had the proper setup, and immediately I was able to properly send & receive.
I'm still researching how all those exceptions got in there (that type of thing makes me buku suspicious I may have caught a bug... ), but that solved the problem.
I did not have to reconfigure Outlook, nor did I have to set up any DNS entries - but this may not be everyones case.
I suggest checking firewall settings for whatever software you personally use.
It's been my experience many times in the past that firewall settings can be improperly setup or corrupted somehow, and is often the culprit behind connectivity issues.
Hope this helps someone, have a great day!