I check four email addresses regularly via Apple Mail. How do I consolidate them to just one account? This is would mainly be for the iPhone, which doesn't have a view all accounts option.
A free yahoo mail account allows you, as far as I know, to set up POP retrieval from other email accounts, so all of them download into that one yahoo account. Also, many, if not most, email services allow you to have all of your messages forwarded to another email address, just check in your preferences with the email provider.