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For what you need to do legally, you'll need to consult a lawyer in your jurisdiction. Laws vary. The rest of this answer is about practical considerations. First, are you on good terms with the...
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#3: Attribution notice added
Source: https://writers.stackexchange.com/a/10014 License name: CC BY-SA 3.0 License URL: https://creativecommons.org/licenses/by-sa/3.0/
#2: Initial revision
For what you need to do _legally_, you'll need to consult a lawyer in your jurisdiction. Laws vary. The rest of this answer is about _practical_ considerations. First, are you on good terms with the person whose email you want to use? Do you want to be on good terms after you publish your work? If so, then _talk with this person_. Nobody likes surprises, and there is a presumption that private correspondence is, well, _private_. (If the email came from a large, well-distributed, archived mailing list, that's a little different -- but I would still ask.) Second, even if you change the names, given a large-enough corpus a person who knows what he's doing can identify the person (to a fair degree of confidence) anyway. Everybody writes with certain "markers" that help to identify their work; what they are varies and you probably don't know you're doing it, but you are. This isn't just spy-agency stuff here; corpus analysis is a standard tool in fields like linguistics and statistics -- and, for that matter, certain software domains. What this means is that scrubbing the names _doesn't_ necessarily anonymize. I recommend that you first talk with the person about your desires, and then work together with that person to transform the email you want to quote in a way that satisfies both of you. This could involve selective quoting, summarizing rather than directly quoting, and/or rewriting passages (that is, you do the rewriting, not the original author).