bug#51733: 27.1; Detect impossible email addresses better

[Robert Pluĭm]

>>>>> On Wed, 19 Jan 2022 15:00:04 +0100, Lars Ingebrigtsen <larsi@gnus.org> 
>>>>> said:

    Lars> Robert "=?utf-8?Q?Plu=C4=ADm?=" <rpluim@gmail.com> writes:
    >> I canʼt recall if this is allowed by the standards or not offhand, but
    >> as youʼre probably well aware, the major email providers allow you to
    >> use UTF-8 characters directly in the display name of email adresses,
    >> without using RFC 2047 encoding. In fact, the last time I did any
    >> testing of this, Gmail *replaced* RFC 2047 encoded non-ASCII
    >> characters with their UTF-8 encoding.

    Lars> Gmail expects you to type in characters representing your name -- they
    Lars> don't expose the wire format.  Why should they?

    Lars> And your address arrived as (wire format):

    Lars> Robert =?us-ascii?Q?=3D=3Futf-8=3FQ=3FPlu=3DC4=3DADm=3F=3D?=

    Lars> which displays as

    Lars> Robert =?utf-8?Q?Plu=C4=ADm?=

    Lars> 😀

Double fun. Iʼd manually rfc2047 encoded that before sending it, so
either gnus or Gmail encoded it again :-)

Iʼve turned off the gnus rfc 2047 for this message, let's see what
happens.

Robert
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