One of the oldest suggested features in the Suggestions section has been to allow checking mail with your email address instead of just the annoying m1234567 username.
DreamHost have now implemented this much wished for feature and are now looking for beta testers to test it out and help them work out the kinks, before they can make the official announcement. All you have to do is switch your m1234567 username to email@example.com. Be aware that this is work in progress so you might have to switch back at some time, while they’re working on it.
By looking at the current feedback in the discussion forum it looks like it works for most people (only two-three problems within the first twenty responses) and the update is very much appreciated.