Think of email as just a little less secure than a postcard in the mail.
Then you'll be fine.
As this was discussed in BOL 1096.
4th amendment says "The right of the people to be secure in their persons, houses, papers, and effects, against unreasonable searches and seizures, shall not be violated, and no Warrants shall issue, but upon probable cause, supported by Oath or affirmation, and particularly describing the place to be searched, and the persons or things to be seized."
Tom was arguing that it doesn't apply to email because email is not in your home. But I don't think that's a very sensible interpretation. "secure in their persons, houses, papers, and effects" it's a list of things that the amendment applies to, it's certainly not saying though that the object must be all the above.
And I certainly think email should apply under 'papers and effects'. The ISP could just as easily be holding physical papers of your letters, and 4th amendment would certainly prevent the government from searching them. It should apply to email too, which at minimum applies as your effects.

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