Attachment events occur when an attached file is being read, written, or opened. These events enable extensions to control access to attachments and provide custom handling behavior. Attachment extensions are useful for providing virus detection and compression of attached files. These extensions are called from the context of the message containing the attachment.
Note Not all attachments are files. Attachment events apply only to attached files. Because attachments can themselves be other messages — that is, messages can contain messages — another context corresponding to the attached message might be created when an attached message is opened.
The following table shows the steps involved in sending a standard message with an attachment. It also shows which component — Microsoft Exchange client or the extension — performs the step and in the case of the client extension, what method is invoked.
The following table shows the steps involved in reading a message and opening its attachment. It also shows which component — the Microsoft Exchange client or the extension — performs the step, and in the case of the extension, shows what method is invoked.
