Hmm, we normally don't just delete user accounts...
Furthermore, noone else can change a user's email address.
Even though not verified, could @Meno25 log in via Wikimedia's SUL and access https://phabricator.wikimedia.org/settings/panel/email/ to change the email address and add a new one?
OK, you can do via an SQL command. What I should have written instead: The web interface does not allow Phabricator admins to change a user's email address (while e.g. Bugzilla allowed it).
Instead of deleting I went for renaming the existing user account from @Meno25 to @Menodisabled (and disabled that account).
I hope that now @Meno25 can create a new Phab account as @Meno25 again, with a valid email address to verify. But as @Menodisabled is still tied to the MediaWiki User account Meno25 I am not entirely sure. If it does not work, I'm willing to completely delete the account.
For the records, Phabricator's printed info for renaming accounts is pretty similar to that for deleting:
"Be careful when renaming users! The old username will no longer be tied to the user, so anything which uses it (like old commit messages) will no longer associate correctly. (And, if you give a user a username which some other user used to have, username lookups will begin returning the wrong user.) It is generally safe to rename newly created users (and test users and so on), but less safe to rename established users and unsafe to reissue a username. Users who rely on password authentication will need to reset their password after their username is changed (their username is part of the salt in the password hash). The user will receive an email notifying them that you changed their username, with instructions for logging in and resetting their password if necessary."