If you log into your email account using MailSuite Pro, you may run into the issue when Inbox content is loaded just fine, but some other folders in the folder list are greyed out and cannot be selected.
That happens because some other email client (or even mail server itself) marked those folders as Unsubscribed - which, in terms of IMAP protocol, means hiding a folder. And typically a folder will indeed be hidden from the list, except those few special folders: Sent, Drafts, Trash and Spam. They're show in the list but can't be selected.
To un-hide folders, open "Manage Folders" screen using the link at the bottom of folder list. To un-hide special folders, click "Setup special folders" and choose "No usage selected" for that particular folder. Then, in the folder list on Manage Folders screen, click the eye icon for that particular folder to un-hide it, and enable it again using "Setup special folders" tool.
If the issue occurs for multiple accounts, there's another option - you can reconfigure your MailSuite Pro installation so that all the folders are displayed, regardless of their status on IMAP server.
To do that, edit
data/settings/modules/Mail.config.json file and set IgnoreImapSubscription to true:
"If true, all the email folders can be accessed, regardless of their IMAP subscription status; also, a tool for hiding\/showing folder is removed from Manage Folders screen"
NB: with this option enabled, it won't be possible to rename folders as the flags are unavailable.