On Sat, Apr 30, 2016 at 12:44 PM, Alice Wonder <alice at domblogger.net> wrote: > > For e-mail sent to people, yes. > > But for what usernames are allowed when creating an account, I don't see why > blacklisting characters that are not allowed in a username is a standards > problem. That's not how the RFC rules are defined. But, rather than argue that point at length, I'd point out that Open Group standards for usernames are simple and will comply with the SMTP RFCs: http://pubs.opengroup.org/onlinepubs/000095399/basedefs/xbd_chap03.html#tag_03_426 That is, [A-Za-z0-9._][A-Za-z0-9._-]