If you have IMAP account setup on mail client such as Outlook, Thunderbird, etc, and some of the folders are not showing in folder list. When you experienced such issue, you may try to:
1) First, login to your webmail by using your email account credentials (usually at e.g. https://webmail.mydomain.com). Click on Roundcube box if the page is not redirect to your inbox page.
Webmail > Mail > Settings > Folders
Toggle the button for which folder you would like to appear in webmail and your mail client IMAP folder list.
2) re-run IMAP query or re-subscribe folders in your mail client setting, follow instructions as per:
https://support.mozilla.org/bm/questions/1363677
Once done. re-sync or send & receive your mail client.
