[jeffbee]

This article says that Gmail can't handle address literals. I personally wrote the IPv6 address literal support for Gmail, so this annoys me. I just tested it and it shortened "[IPv6:2001:etc:etc::192.etc.etc]" down to "@2001" then generated an extremely terse mail delivery subsystem notification that I've never seen before. Which is why you should never just rewrite software without understanding why all the test cases are in the test suite!

[farfatched]

Could they have consciously chosen to remove that functionality?

E.g. to simplify code, or if they wanted all mails to have a domain (if, for example, they wanted to integrate with reputation systems that were domain oriented)?

[jeffbee]

Based on the incredibly basic bounce message, I suspect the problem is that the frontend eats the address before it even gets to delivery.

To your question, yes any product decision is possible, but enterprise/government people are surprisingly demanding about this stuff working because they have extremely weird requirements for routing mail to and through legacy systems. So I bet this still works at the mailer level and is broken in the UI.

[jcranmer]

I chuck IP address literals (both IPv4 and IPv6) on the list of things that you should care about for email if you're writing an MTA or an MUA but should otherwise generally not care about supporting if you're using email for something else (e.g., as a UID for login).

[farfatched]

> but enterprise/government people are surprisingly demanding about this stuff working because they have extremely weird requirements for routing mail to and through legacy systems. So I bet this still works at the mailer level and is broken in the UI

Interesting context, thanks.

[thwarted]

> "[IPv6:2001:etc:etc::192.etc.etc]"

I'm trusting this is a throwaway example and that you used a real IPv6 address literal in this test, without the "IPv6" and with only colons and no dots (unless you mean to use v4 mapped address with dots)? Because this IPv6 literal is so malformed that I'm hardly expecting it to do something sane and changing that to "@2001" is nasal-demons quality undefined behavior. I tried with this exact literal and it let me send it but then there was a tiny red pop-up at the top of the gmail interface that said "could not be delivered, check your network connection" (which is odd; the same kind of pop-up that appears in gray when you legitimately are not connected to the internet) and it ended up in my drafts with the To: field empty.

I just tried to send a message to a "test@[" my current IPv6 address "]", and gmail told me

    Error
    The address "test@[«redacted»]" in the "To" field was not recognized.
    Please make sure that all addresses are properly formed.

This address doesn't have an MDA listening on it, but it didn't accept it enough to give me a non-delivery notification, it didn't even let me send it. gmail did accept an IPv4 address literal in brackets, although it hasn't given me back a non-delivery notification. What it stuffed into my Sent folder for this message has the square brackets stripped and the IPv4 address appears right after the @.

[jeffbee]

All address literals other than IPv4 must be prefixed by a tag, such as "IPv6:". The form that I gave is a syntactically valid v6v4 address literal.

https://datatracker.ietf.org/doc/html/rfc5321#section-4.1.3

[thwarted]

Interesting, TIL. That makes the conversion to @2001 even stranger.