I use MailKit for creating a folder. This is simple, I can e.g. call CreateFolderAsync (if I want to async way) on the parent folder.

    public async Task<IMailFolder> GetOrCreateFolder(string folderName)
    {
        var rootFolder = await authenticatedClient.GetFolderAsync(imapClient.PersonalNamespaces[0].Path);
        var existingFolders = await rootFolder.GetSubfoldersAsync();
        var matchingFolder = existingFolders.FirstOrDefault(folder => folder.FullName == folderName);

        if (matchingFolder == null)
        {
            matchingFolder = await rootFolder.CreateAsync(folderName, true);
        }

        return matchingFolder;
    }

However, if I pass in a string like GetOrCreateFolder("folder/subfolder") or GetOrCreateFolder("folder.subfolder") (because I later found out many IMAP servers apparently use . as a directory separator sign. This is defined/returned by the server in IMailFolder.DirectorySeparator e.g.).

Both will throw an exception if you try this (“The name is not a legal folder name”):

System.ArgumentException
  HResult=0x80070057
  Nachricht = The name is not a legal folder name. Arg_ParamName_Name
  Quelle = MailKit
  Stapelüberwachung:
   bei MailKit.Net.Imap.ImapFolder.QueueCreateCommand(String name, Boolean isMessageFolder, CancellationToken cancellationToken, String& encodedName)
   bei MailKit.Net.Imap.ImapFolder.CreateAsync(String name, Boolean isMessageFolder, CancellationToken cancellationToken)
   // ...

  Diese Ausnahme wurde ursprünglich von dieser Aufrufliste ausgelöst:
    MailKit.Net.Imap.ImapFolder.QueueCreateCommand(string, bool, System.Threading.CancellationToken, out string)
    MailKit.Net.Imap.ImapFolder.CreateAsync(string, bool, System.Threading.CancellationToken)

You can obviously hardcode the creation of the first folder, and then the second, but this is really not flexible at all.
I mean, after all, mkdir on Linux e.g. also supports creating multiple folders at once, why can’t we here?

So, how can I just make this work?