Add Container Option

MIME messages consist of one or more body parts. In the simplest case, these body parts are strung together sequentially. However, you can create body parts which, in turn, contain other body parts. These are referred to as Container body parts. The section immediately below describes the four types of containers you can select.

Mixed

Select this option to create a Mixed container for one or more body parts. There are no rules on what types of body parts may be put in this container form. This is a "generic" container.

Message Digest

Select this option to create a Message Digest container. This type of container is used to contain a group of one or more complete MIME messages (also known as RFC822 messages), for example a group of messages being forwarded to another recipient.

Alternatives

Select this option to create an Alternatives container. This type of container holds groups of two or more body parts that contain equivalent information, using different formatting of access methods. This option is useful if you aren't sure what level of MIME capability the recipient(s) of your message have, if you aren't sure whether they have MIME capability at all, or if you just wish to give them a choice.

In an Alternatives container, each body part contains the same information, accessed or formatted differently. The first body part contains the simplest version, typically plain ASCII text. The last body part contains the preferred version.

For example, if you send a message containing Enriched Text, a version of the text with the Enriched Text attributes stripped out should appear at the front of the message. If you send a message containing GIFs, or other types of binary attachments, these cannot be converted to ASCII. However, any explanatory text you type into the message will be visible.

Another way an Alternatives container can be used is to provide alternate access methods to a file. For example, when attaching a file to a message the most desirable way of doing so is as a Local file. However, this is only available to recipients on the same local network. Attaching a file using FTP access is a more universal, yet slower method of attachment. To cover both cases, you could build an Alternatives container and put two file attachments in it, each referring to the same file. The first attachment would be FTP type and the second (preferred) would be Local file type.

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NOTE:
This option gives you explicit control over creating an Alternatives container. However, you will probably find it easier simply to compose a message normally, then click the Both if necessary button at the bottom of the Composition window. The both in this case refers to a message with both plain text alternative and MIME parts. Ishmail will automatically build the Alternatives container for you, and put a plain ASCII text version of your message as the first body part.

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Parallel

Select this option to create a Parallel container.This type of container holds groups of two or more body parts which are considered related. The recipient of the message should try to "show" the body parts together. For example, an MPEG video clip and an Audio clip could be put in a parallel container. The recipient's mail tool should try to show the video clip while simultaneously playing the audio clip.

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NOTE:
While the idea of a Parallel container is good, in practice it is difficult to implement well. This is because programs external to Ishmail are used to show various body parts. In the example of a video clip and an audio clip, the MPEG viewer program usually takes several seconds to start up, while the audio clip can be played immediately. So, even though Ishmail could launch both programs simultaneously you will usually hear the audio clip long before you see the video.

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