[x1798DE]

One problem with this is that if an instance is a "mailing list", it's currently not possible to join multiple mailing lists with the same e-mail address. That said this would not be as big a problem with e-mail addresses as it is in Mastadon; as WorldMaker mentions, the analogy breaks down because of the public feed - if you want to create an alias, you need to duplicate your public feed, and if you have things like the federated feed and hashtag search, you're going to end up with a lot of duplicated content out there.

If you had a lot of people cross-posting to different mailing lists with similar subscriber lists, I imagine people would be really annoyed if they had no way of merging your duplicated content.