Anything not deleted will remain on the server, and appear in the messages listing next time you check your mail. This is accessible in the message edit window. It will package up the message you are working on, send it to the mail server to be forwarded to its destination, and leave you with a blank window. Trouble in this window usually indocates that there is a problem with the network on your computer, and less often that there is a problem with the mail server. The icon gives a clue to what this means.
Email is generally text only.
When you attach a file to an email message it is encoded so that it appears as text to the email systems between you and the recipient. There are a number of different schemes for doing this encoding, and this leads to one of the more troublesome areas of email -decoding. Most of these formats include a message at the top of the file that lets you know how the contect is encoded. When you receive an attached message in POPMail Lab it will automatically try to decode it for you when you save the message. It is a good idea to let them know what sort of file you are sending in the email message to which the file is attached.