Some folders are not synchronized

There is no assistance apparently, there is no answer to the many problems encountered by users.
Main problem of many people have is the synchronization, some folders are not
strangely synchronized, even if the operation is repeated.
Messages are in the webmail, not in EmClient, it does not see them. Very strange, even in the absence of rules or filters.

Can you share a little more information?  Is your email provider Microsoft (e.g.,, Hotmail) and what protocol are you using (IMAP, Exchage)?.  I have heard of many problems using IMAP with Exchange accounts.

If a gmail account, do you have all the folders in the gmail settings det to “Show in IMAP”?