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Spamgourmet (https://www.spamgourmet.com, https://github.com/spamgourmet/spamgourmet), free, has always worked well for me though these days I tend to just use the disposable addresses built in to Fastmail. Addy.io, (https://addy.io/), free/paid, is a newer offering with some nifty features like automatic PGP encryption.