Gets the expected length (in bytes) of the source data of the message being downloaded.
The expected length (in bytes) of the source data of the message being downloaded, or -1 if no estimation can be made.
This property can be used to evaluate download progress of the current message being downloaded. However, its value is not 100% accurate because it's taken from the message size as reported by the server while actual length of the server response containing the message data is always greater (by 1-2%) due to presence some additional information in the response.
Note If partial messages are downloaded (such as message headers), this property returns -1, since the POP3 protocol has no feature to learn the length of a message header without downloading it. Only lengths of entire messages can be obtained. However, usually it's not a problem - since a message header is usually short, it is, anyway, received in a single network operation (which usually delivers 4-8 Kbytes of data).
Pop3MessageDataChunkReceivedEventArgs Class | MailBee.Pop3Mail Namespace