If you attach a file to an email message being worked on, and then later right-click on that attachment and choose “Remove,” although that file is removed as an attachment, the file itself is still in use, not internally closed, or something along those lines. That is, if you open that now-"Remove"d attachment in another program, you can’t save the file as itself, because it is marked by the O/S as being in use.
This in-use condition of the "Remove"d attachment changes to a not-in-use condition if the email message is actually sent, or if the email message is closed and saved as a Draft message, or if the email message being worked on is discarded.
I don’t think this is a situation of the software’s working as intended, so I thought I’d report this behavior.
Windows Vista Home Premium SP2
eM Client 5.0.17944.0