Percent encoding for special characters in email address

[Dumluregn]

Type of report

Feature request

Provide description of the new feature

Extracted from #2138, as mentioned there:

According to [RFC5322], the characters "?", "&", and even "%" may
occur in addr-specs. The fact that they are reserved characters is
not a problem: those characters may appear in 'mailto' URIs -- they
just may not appear in unencoded form. The standard URI encoding
mechanisms ("%" followed by a two-digit hex number) MUST be used in
these cases.

Source: RFC 6068

So we should either percent-encode special characters, or perhaps inform our users that they should handle it.
I wonder if change on our side is possible at all (although it's very easy to do) as this can cause some issues for users who won't notice it and start receiving encoded addresses. On the other hand we already encode email subject and body, so maybe it's not such a big deal.