I received mail earlier today from Google announcing support for DKIM for all Google Apps editions. My boss has always complained that he couldn't send email to or receive email from his boss, and the IT people at his boss' company always refused to check their in-house email server for problems and keeps telling me to check my email server for problems.
Occam's razor moment. An in-house email server with hundreds of users vs. Google Apps. What are the chances the problem is on my end? DKIM doesn't really have anything to do with inability to receive mails, but I like to throw acronyms at my boss, so, I enabled DKIM on Google Apps and set my DNS accordingly, and on another tab, I was doing user transitions to the new Google Apps infrastructure. While I was doing this, I suddenly noticed on the Dashboard I can request for more users. The request for more users button was disabled a few years ago when Google Apps started the Premier Edition (now simply called Google Apps for Business) and since I already have 200 users I never actually needed more users. (Unlike new Google Apps users that can only get 50 users, I've been using Google Apps since 2006 and started with 100 users, and I've requested for 200 users in 2007.)
To make sure I wasn't imagining things, I googled and found this TechCrunch article, which is exactly what my dashboard looked like earlier. And just to make sure I'm not dreaming, I immedidately requested for 100 more users.