I don't think so, depends on where you live and the laws that apply there. It's probably easier to seize a home server than it is to hassle a company to divulge its contents.
I think it's the other way round in the US. Conventional email hosting providers are definitely not protected by the 4th. Also for political activists, actually raiding their homes is a dead giveaway whereas leaning on companies can be done quietly.
Should be easier to just encrypt all the email.
Either by encrypting the HDD or by automatically encrypting all ingoing email with you public GPG key (Saw a perl script for this in a blog)
