Sending MIME emails using PHP (1)_PHP Tutorial

Author: Kartic Krishnamurthy Translator: limodou

Tired of sending those tedious text notifications and letters to your friends and clients? Have you ever considered sending attachments or
embedding HTML in emails?

The answer is MIME. The next few pages explain the basics of MIME, creating MIME-compliant messages, and then finishing with a working PHP (the most popular development language today) class that implements sending MIME-compliant messages. mail. Note that references to calling script, caller, etc. refer to the script using the class to be developed, client/MUA, etc. to refer to the mail-reading client or mail-using agent.


Some MIME basics
MIME stands for Multipurpose Internet Mail Extensions. MIME extends the basic text-oriented Internet mail system to include binary attachments in
messages.

MIME takes advantage of the fact that RFC 822 imposes some restrictions on the content of the message body: the only restriction is that it can only use simple
ASCII text. So, a MIME message consists of a normal Internet text email with some special RFC 822-compliant
header and a formatted message body (an attachment represented by a subset of ASCII). These MIME headers provide a special
way of representing attachments in emails.

Anatomy of MIME messages
An ordinary text email message contains a header part (To: From: Subject:, etc.) and a body part (Hello Mr.,
, etc.). It is not surprising that a MIME-compliant message also contains a header. Each part of the message is called a MIME segment, and each segment is also prefixed with a special header
. MIME mail is just an extension based on RFC 822 mail. However, it has its own set of RFC specifications.


Header field
MIME headers are generally divided into MIME information headers and MIME segment headers based on their location in the mail packet. (Translator: The MIME header refers to the header of the entire email
, while the MIME segment header is only the header of each MIME segment.)

MIME headers include:

MIME-Version:
This header provides the version number of the MIME used. This value is conventionally 1.0.
Content-Type:
It defines the type of data so that the data can be processed appropriately. Valid types are: text, image, audio, video,
applications, multipart and message. Note that any binary attachment should be called application/octet-
stream. Some use cases for this header are: image/jpg, application/mswork, multipart/mixed, just to name a few
.
Content-Transfer-Encoding:
This is the most important of all headers as it describes the encoding performed on the data and will be used by the client/MUA to
decode the attachment. For each attachment, you can use one of 7bit, 8bit, binary, quoted-printable, base64 and custom encoding methods. 7bit encoding is a commonly used encoding method used on the US ASCII character set, that is, keep it as is. 8bit and
binary encoding are generally not used. For human-readable standard text, if the transmission is to be protected through a gateway that affects the format,
you can use quoted printable . Base64 is a general-purpose method that provides
a no-brainer when deciding which encoding method to use; it is typically used on binary, non-text data. Note that any non-7bit data must be encoded with a pattern
so that it can pass the Internet mail gateway!
Content-ID:
This header is useful if Content-Type is message/external-body or multipart/alternative. It is beyond the scope of this article.
Content-Description:
This is an optional header. It is a free text description of the content of any piece of information. The description must use us-ascii code.
Content-Disposition:
An experimental header used to provide a hint to the client/MUA to decide whether to display attachments inline or as separate attachments.
MIME section header (the header that appears in the actual MIME attachment part), except the MIME-Version header, can have any of the above header fields. If a MIME header is part of a chunk, it applies to the entire body of the message. For example, if Content-Transfer-Encoding appears in a message header, it applies to the entire message body, but if it appears in a MIME segment, it "only" applies to that segment.