Dotless domains

[John Levine <[e-mail]>]

A friend* wonders about the SMTP treatment of addresses in TLDs.
Historically there have been a smattering of such addresses, most
famously n@ai, and there are 21 TLDs with MX records, but spot
checking shows that most appear to be config mistakes, with the MTAs
not actually accepting mail to postmaster@tld.

If ICANN does what they claim they're going to do and starts selling
thousands of new TLDs, we're likely to see a lot more dotless
addresses.  bob@aol, anyone?

As best I understand it, the prose description of addresses in 2821
allowed TLDs in addresses, but the ABNF didn't.  In 5321 the ABNF
changed to match the prose.  Although the DNS allows you to put a dot
at the end of a domain name to make it clear that it's an absolute
address, SMTP has never allowed that.

My impression is that in the real world, mail addressed to
postmaster@va is far more likely to be rewritten to
[e-mail] than delivered to the Vatican (which, as it
happens, will accept it.)  Mail addressed to postmater@va. with a dot
isn't valid under 821, 2821, or 5321, so some MTAs accept it, some
reject it.

Is the current situation with TLDs deliberate, or was the change in
5321 just aesthetic tidying up?  Is there any reason not to permit a
trailing dot in 5321-bis to bring it in line with DNS rules?

Regards,
John Levine, [e-mail], Primary Perpetrator of "The Internet for Dummies",
Information Superhighwayman wanna-be, http://www.johnlevine.com, ex-Mayor
"More Wiener schnitzel, please", said Tom, revealingly.

* - no, really