I don’t know if this has changed since January but this appears to only half work when the enable markdown linkify setting is enabled.
The regular expression works perfectly to censor the text but an email address is parsed and turned into a mailto link first, exposing the email address in the HTML.
E.g.
<a href="mailto:someone@example.com">■■■■■■■■■■■■■■■■■■■</a>