What is the encoding in imap?

Question

Perl

I'm trying to decode mail received via imap using perl (I use Net::IMAP::Simple)

I get the following lines: Lebedev's

=?UTF-8?B?RGF2aWQgS3VyZXh5YW4g0L/RgNC40LPQu9Cw0YjQsNC10YIg0JLQsNGBINGB?=

decoder coped with the decoding and wrote that it is base64

But if you try

use MIME::Base64;
print decode_base64('=?UTF-8?B?RGF2aWQgS3VyZXh5YW4g0L/RgNC40LPQu9Cw0YjQsNC10YIg0JLQsNGBINGB?=');

then the output is empty.

Answer 1

This is MIME-B, look for how to work with it.

Answer 2

This is base64. It is necessary to decode what is after after "=?UTF-8?B?"
Answer: "David Kurexyan invites you with"

Answer 3

This is decoded with Encode::MIME::Header.
In addition to B (base64), there may also be Q (quoted-printable).

Answer 4

First, not in IMAP, but in the mail header. This is how all non-ASCII mail headers are arranged - only characters with the most significant bit 0 are allowed inside, i.e. UTF-8 is not directly valid; it is encoded in BASE64 and thus placed in the headers.
Secondly, even without knowing the answer, it would be logical to assume that =?UTF-8?B? is a "preamble" describing the format of the subsequent data, from? before? (which is not a base64 encoded character).
Thirdly, if your header looks like
Subject: =?UTF-8?B?bla-bla-bla?=
(spaces) =?UTF-8?B?bla-bla-bla?=
then all these lines need to be unpacked independently and then do the concatenation.
In general, read RFC5321 and 5322. The specific pearl module was suggested above.