Text.UTF7Encoding?
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Понятно ж в какой кодировке вроде ...
авторABSTRACT
IMAP mailbox names are encoded in a modified UTF7 when names contains international characters outside of the printable ASCII range. The modified UTF-7 encoding is defined in RFC2060 (section 5.1.3).

There is another CPAN module with same purpose, Unicode::IMAPUtf7. However, it works correctly only with strings, which encoded form does not contain plus sign. For example, the Cyrillic string \x{043f}\x{0440}\x{0435}\x{0434}\x{043b}\x{043e}\x{0433} is represented in UTF-7 as +BD8EQAQ1BDQEOwQ+BDM- Note the second plus sign 4 characters before the end. Unicode::IMAPUtf7 encodes the above string as +BD8EQAQ1BDQEOwQ&BDM- which is not valid modified UTF-7 (the ampersand and the plus are swapped). The problem is solved by the current module, which is slightly modified Encode::Unicode::UTF7 and has nothing common with Unicode::IMAPUtf7.

RFC2060 - section 5.1.3 - Mailbox International Naming Convention
By convention, international mailbox names are specified using a modified version of the UTF-7 encoding described in [UTF-7]. The purpose of these modifications is to correct the following problems with UTF-7:

1) UTF-7 uses the "+" character for shifting; this conflicts with the common use of "+" in mailbox names, in particular USENET newsgroup names.

2) UTF-7's encoding is BASE64 which uses the "/" character; this conflicts with the use of "/" as a popular hierarchy delimiter.

3) UTF-7 prohibits the unencoded usage of "\"; this conflicts with the use of "\" as a popular hierarchy delimiter.

4) UTF-7 prohibits the unencoded usage of "~"; this conflicts with the use of "~" in some servers as a home directory indicator.

5) UTF-7 permits multiple alternate forms to represent the same string; in particular, printable US-ASCII chararacters can be represented in encoded form.

In modified UTF-7, printable US-ASCII characters except for "&" represent themselves; that is, characters with octet values 0x20-0x25 and 0x27-0x7e. The character "&" (0x26) is represented by the two- octet sequence "&-".

All other characters (octet values 0x00-0x1f, 0x7f-0xff, and all Unicode 16-bit octets) are represented in modified BASE64, with a further modification from [UTF-7] that "," is used instead of "/". Modified BASE64 MUST NOT be used to represent any printing US-ASCII character which can represent itself.

"&" is used to shift to modified BASE64 and "-" to shift back to US- ASCII. All names start in US-ASCII, and MUST end in US-ASCII (that is, a name that ends with a Unicode 16-bit octet MUST end with a "- ").

For example, here is a mailbox name which mixes English, Japanese, and Chinese text: ~peter/mail/&ZeVnLIqe-/&U,BTFw-
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