I've seen email problems for ages.
On my previous host, I might have seen a mail connection error every 4 to 6 weeks; at DH, it's been averaging from once every 5 days all the way down to once a day or more. Not to mention domain problems, web problems and other, broader downtime.
I'm starting to get very skeptical about this business of having DH management people in one location and having rented data center space spread out in distant locations, across a number of different providers.
I'd say it's highly probable that the local IDC people do not have the same attitude toward service / emotional investment that the DH people do (which seems to be excellent), and that the DH people are just not able/willing to proselytize the local yokels to the DH mindset, or at the very least to crack the whip.
There was an announcement recently about upstream connectivity downtime, in which DH said they were going to have a meeting with the IDC (Softaware, IIRC) to see what they have in place re: connectivity redundancy (apparently not much).
I haven't heard anything more on that... I'm hoping that meeting did happen... and that DH can get a handle on all of these repeated outages.
The number of major outages I've seen since I've been here has probably been about 5 times that at my previous host, and the number of total outages has probably been something like 15 to 20 times higher.
I thought service was really degrading at my old host, so I moved. I've started to regret that decision.
I'm praying that the mail server upgrade will eliminate the constant niggling mail outages, but I'm not holding my breath.