Firstly, I will state that I have had no problems with mail from my DreamHost accounts being blocked, but I tend to use my ISPs SMTP server for sending, I find this leads to less problems of this type.
I am not sure DreamHost would be the ideal solution to your problem, as there are often reports here on the forums of mail from the DreamHost mail servers being blocked. This is invariably caused by the mail servers somehow being placed on blacklists and it sometimes takes a while for DreamHost to have their mail servers removed from the lists.
If mail is really important to you, I think you should seriously look into obtaining your mail services from a company that specializes in providing only mail services, there are quite a few of these around and they are generally not too expensive.
Edit: I just re-read your post and I know see that you are concerned about incoming mail, not outgoing, being blocked, I don’t think you will have that particular problem at DreamHost, but I still advise you to have a serious look at a dedicated email service.
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