On the surface this seems like a good idea, in practice most people will quickly recognize that adversaries could easily use this to follow your purchases around by looking for your “[email protected]”. It smells like a honeypot to corral new Monero (or naive/ignorant older ones).
Consider this, there are no emails ever sent encrypted unless the user explicitly does/enables this, services such as protonmail claiming e2e is ridiculous because the keys do not belong to the user(e2e on chat clients the user installs on their own devices is actually productive in this sense because the keys are actually with the user even if they do not know this) they are held by the server owners thus no real security whatsoever if “the state” decides they want to read your emails for whatever arbitrary reason. This default method easily finds itself contributing to the data trove of not only marketing material but, surveillance being purchased by the american government in wholesale. This is of course being the tip of the iceberg.
It would seem beneficial to the users if anonymity was maintained by randomly creating an “[email protected]”, then following that step and requiring the users send you their public PGP key so that you can by default encrypt the messages going to them. If you want to take it a step further, exclude yourself from the information shared by both parties by sending them a link or similar that requires them to submit their public PGP key to encrypt before anything happens and now you truly have no middle man other than bringing the 2 parties together.
Our presentation of this may be a slightly bit convoluted but, the gist is keeping things random at the “signup” (not really a signup in so much as a random generation of whatever), then after that make it mandatory to encrypt the emails going out because you have no control over who can read what when it leaves you, especially when it is in plain text as a majority of emails are.