Most people in our company have iPhones - and while we can receive our (dreamhost) account emails -we cannot send mail OUT. No problems whatever with other accounts, such as gmail.
I was able to solve the out-going mail problem on the newer accounts by "accepting" or hitting "continue" when the dialog came up that the dreamhost outgoing mail server host was invalid (or something similar). I assume this is related or similar to when I am setting up dreamhost email on a new computer - and I always have to accept the browsers dialog that the Dreamhost certificate is invalid (therefore have to bypass it).
We have quite a few dreamhost accounts, and this tends to only happen on the oldest one, which has always acted somewhat different than the accounts that were created more recently. For instance, on the older ones, I have issues in squirrel-mail opening and purging the junk folder.
Any help greatly appreciated! Every day I become more convinced we should all just switch to gmail!