You should have recieved specific instructions on how to do this from Dreamhost support upon completion of domain transfer. But then again, if you can't access your email and you didn't set an alternative account, you wouldn't know that they sent it. A classic example of a catch 22 situation, I believe.
Anyway, try the following settings in your mail client:
Replace yourdomain.com with your actual domain.
Use your username and password supplied to you (the same ones you use to access FTP and SSH) to access your email. For SMTP services (outgoing mail), you will either need to contact support, because I'm not sure if this is allowed as default for all domains. Otherwise, use your ISPs outgoing mail servers for now.
As for your old mail from your previous account; most likely unless you downloaded all mail before transferring your account, your mail will have been deleted. Most system providers delete your mail and everything else associated with your account once you sign off. Partly due to security measures. You should have been warned and you should have downloaded all your mail before the move.
Let me know how this goes, and if you need more help. It might be an idea to start an emegrancy alternative account with Hotmail or another free service provider. You can then ask Dreamhost to copy all important announcements and support queries sent from the support staff to both accounts just to make sure you recieve them. Especially if Dreamhost mail is playing up.
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