You can get the folder properties using zmmailbox:
$ zmmailbox -z -m
account@domain.com -v gf /Inbox
It should show something like this:
{
"color": "defaultColor",
"contentSequence": 1,
"defaultView": "message",
"flags": "*",
"grants": [],
"id": "2",
"imapItemCount": 4,
"imapMODSEQ": 7453,
"imapUIDNEXT": 489,
"imapUnreadCount": 0,
"isCheckedInUI": false,
"isExcludedFromFreeBusy": false,
"isSyncEnabled": false,
"isSyncFolder": false,
"isSystemFolder": true,
"itemCount": 4,
"name": "Inbox",
"parentId": "1",
"path": "/Inbox",
"pathURLEncoded": "/Inbox",
"size": 77377,
"subFolders": [],
"unreadCount": 0
}
Notice the "flags": "*" field. Generally, when a folder is subscribed, it will show you a "*". If it is not, the flags field will be empty or it will have other non-related settings. You can change this by running zmmailbox mff (modify folder flag):
$ zmmailbox -z -m
account@domain.com mff /Folder "*"
And refresh your IMAP client. I have tested this with Thunderbird and it works. Exactly what I was looking for.