Text and HTML message bodies are encoded with the quotedprintable mechanism by default. Message headers
are also encoded with the quotedprintable mechanism if you do not specify base64 in setHeaderEncoding()
.
All other attachments are encoded via base64 if no other encoding is given in the addAttachment()
call or assigned to the MIME part object later. 7Bit and 8Bit encoding currently only pass on the
binary content data.
Header Encoding, especially the encoding of the subject, is a tricky topic. Zend_Mime
currently implements
its own algorithm to encode quoted printable headers according to RFC-2045.
This due to the problems of iconv_mime_encode
and mb_encode_mimeheader
with regards to certain charsets. This algorithm only breaks the header at spaces, which might lead to headers
that far exceed the suggested length of 76 chars. For this cases it is suggested to switch to BASE64
header encoding as the following example describes:
// By default Zend_Mime::ENCODING_QUOTEDPRINTABLE $mail = new Zend_Mail('UTF-8'); // Reset to Base64 Encoding. $mail->setHeaderEncoding(Zend_Mime::ENCODING_BASE64);
Zend_Mail_Transport_Smtp
encodes lines starting with one dot or two dots so that the mail
does not violate the SMTP protocol.