Thank you for the answer.
Yes, I see, there are a lot of queries. I will make some test but I think that "ALL" and "SINCE" are enough for me.
Anyway can I ask you some other question?
The "SINCE" query accepts only a date in 17-Dec-2012 format? I receive a Bad or not correct search query exception if I try to use something else.
Why get a FormatException with the code ImapX.MessageCollection messages = client.Folders["INBOX"].Search("SINCE 17-Dec-2012", true)?
I skipped this problem using ImapX.MessageCollection messages = client.Folders["INBOX"].Search("SINCE 17-Dec-2012", false) but when I read some messages I have the same exeption on the method Message.Process() exactly when I'm reading the email with the attachment that I need to download.