What means Zend_Mime::ENCODING_8BIT when sending mails with Zend_Mail?

In the example for Zend_Mail on http://framework.zend.com/manual/en/zend.mail.attachments.html they use ENCODING_8BIT but searching for what that might be sends me to http://msdn.microsoft.com/en-us/library/ms526992%28EXCHG.10%29.aspx were (and this sounds logical to me) it is explained that 8bit encoding does not make sense for emails.

Edit:

When I use this encoding for a mail with an attachment, I receive the mail with a corrupted attachment in my mail software (Thunderbird)

In which ca开发者_开发技巧ses does it make sense to use ENCODING_8BIT?

As everybody said, ENCODING_8BIT represents the Content Transfer Encoding. Basically, 8BITMIME is used for Internationalization. It's using a 8-bit character sets and therefore, allow you to send any character supported in the UTF8 charset.

In general, non-MIME mailers send 8-bit data but do not include any MIME headers to mark the message as 8-bit data. MIME mailers should cope with this without any problems. [source]

So basically there is not really a case where it makes sense to use ENCODING_8BIT over another encoding since emails in UTF8 are a standard today. Also, note that most of the MTAs (Message Transfer Agent, such as Postfix, etc.) automatically force the encoding to 8BITMIME (UTF-8).

Here is a good resource about the 8BITMIME encoding.

The 8BITMIME extension has two effects in practice:

• The client will avoid Q-P conversion.
• The client may add extra information at the end of a MAIL request: a space followed by either "BODY=7BIT" or "BODY=8BITMIME".

Zend_Mime::ENCODING_8BIT sets the Content-Transfer-Encoding.
The Content-Transfer-Encoding defines methods for representing binary data in ASCII text format.
The use of Zend_Mime::ENCODING_8BIT in the example is a Bug.

For sending Attachments you should always use Zend_Mime::ENCODING_BASE64

Not for email but for attachements. If you take a look on the RFC 2045 at page 7:

RFC2045

"Binary data" refers to data where any sequence of octets whatsoever is allowed.