MailKit - FolderCache and deleted folder

Question

I am in a situation where I have two clients (ClientA and ClientB) connected to IMAP server. ClientA is running mailkit. When I delete or move a folder with ClientB, mailkit client is getting error on attempt to open or fetch messages from the deleted folder. Actually, I am getting disconnected from the server when i try to fetch message from a deleted folder(I guess that is the expected behavior from the server), because of that I am trying to detect if the folder I am about to execute command to, still exists.

I see mailkit uses FolderCache and when I use GetFolder method even after I reconnect the client, I am still getting IMailFolder reference for the deleted folder when I use GetFolder(string path) method. To avoid the FolderCache, I am creating a new instance of MailClient each time I am about to synchronize remote folders to avoid having not existing folders in the cache. I would like to know if that is recommended approach in that situation?

UPDATE:

So, I am now using GetSubfolders command and I can see a LIST command is sent to the server. However it seems there is an issue with that command in the following scenario:

ClientB is deleting a folder INBOX.spam.op, ClientA is trying to move folder with path INBOX.spam.op.folder1. What happens is - the server is creating a new folder INBOX.spam.op with Attributes NonExistent. That is the expected server behavior in order to create folder with path INBOX.spam.op.folder1

But see what happens with Mailkit when I used GetSubfolders on INBOX.spam - I am getting an instance of IMailFolder with Name = "op", Attributes = a mix of the new attributes NonExistent and the attributes of the old "op" folder (the folder in the FolderCache). UidValidity should be 0 for NonExistent but it is the same as the UIDValidity of "op" folder in the FolderCache even if the server response is this

C: A00000102 LIST "" "INBOX.spam.%" RETURN (SUBSCRIBED CHILDREN STATUS (UIDVALIDITY)) S: * LIST (\NonExistent \HasChildren) "." INBOX.spam.op S: A00000102 OK List completed (0.001 + 0.000 secs).

I tried to inherit ImapClient and add my own method GetFolderNoCache(string path) but this doesn't work, because of the internal classes. Any other suggestions?

jstedfast jstedfast · Accepted Answer · 2017-06-30T22:00:08

What you want to do is get the top-level folder from the namespace. Then, using that ImapFolder object, get the list of its children (and so on if you are trying to see if a deeply nested folder).

var toplevel = client.GetFolder (client.PersonalNamespaces[0]);
foreach (var folder in toplevel.GetSubfolders ()) {
    // look for the folder you are interested in...
    // if it's not here, then the folder has been deleted
}

MailKit - FolderCache and deleted folder

1 Answers