Check if imap folder exist using MailKit

Question

I'm trying to move mails to another folder but i can´t find a simple way to check if target folder exists, i presumed that the given folder path is a root folder, i try with this:

public void MoveMessages(Config accountInfo, List<int> uids, string 
   sourceFolderName, string targetFolderName)   
{
            ValidateAccountInfoConfiguration(accountInfo);
            using (var client = new ImapClient())
            {
                Authenticate(accountInfo, client);

                var sourceFolder = GetSourceFolder(sourceFolderName, client);
                sourceFolder.Open(FolderAccess.ReadWrite);
                var topLevelFolder = client.GetFolder(client.PersonalNamespaces[0]);
                var topFolders = topLevelFolder.GetSubfolders();
                var targetFolder = topFolders.FirstOrDefault(folder => folder.Name == targetFolderName);
                if (targetFolder == null)
                    targetFolder = topLevelFolder.Create(targetFolderName, true);
                var uidsToMove = GetUniqueIds(sourceFolder, SearchQuery.Seen).Where(uid => uids.Any(uidToMove => uidToMove == uid.Id)).ToList();
                sourceFolder.MoveTo(uidsToMove, targetFolder);
                sourceFolder.Expunge(uidsToMove);

            }
        }

in the documentation the IMailFolder interface containts Exists property but when i try to get the folder using IMailFolder.GetFolder("pathToFolder") if the folder doesn't exists then a folderNotFound exception is throwed so i can't understand the use case of Exists propety, i missing something? or my current implementation is the right way to achieve get the target folder?

Thumbsdown

JFYI: Expunge is not mandatory: MailKit automatically tries to choose the best solution. If the IMAP server supports the move command, expunge is unnecessary anyway. See: github.com/jstedfast/MailKit/issues/160#issuecomment-79290966 – Anschluss

Answer 1

Your current implementation is the correct way to do it.

The Exists property is useful for some IMAP servers that support having leaf-node folders that are missing a direct parent, for example (which means that the parent folder would have Exists == false).

I've only ever seen this with IMAP servers that use MailDir as their storage format because of the way it creates folders.

Normally you have a tree of folders like this:

toplevel
toplevel/sublevel
toplevel/sublevel/leaf-node

Each folder has to exist all of the way down the tree.

But MailDir doesn't use a UNIX or DOS directory separator, it uses '.', so you could have the following list of folders:

toplevel
toplevel.sublevel.leaf-node

In the above example, there is no toplevel.sublevel folder, but it would appear in the tree of IMailFolder nodes... therefore, there needed to be an Exists property.

Fayefayette

Thanks for the explanation @Fayefayette , now i got it! :) – Thumbsdown

Google Labels can also do this. If you make a label with a "/" in the name, you end up with virtual parent folders. – Stichomythia

Answer 2

As an alternative to downloading the full list of folders, there's this:

public async Task<bool> FolderExistsAsync(ImapClient c, string path) {
    try {
       await c.GetFolderAsync(path);
    } catch (FolderNotFoundException) {
        return false;
    }
    return true;
}

(Although I don't like using a try/catch block for 'normal' control flow)

Kalliekallista