Folders missing from Mail

Thanks for your assistance. I figured it out! I had exceeded the number of folders/mailboxes allowed within our Mail account on the Mac. I went on to our ISP server and viewed the emails/folders there. I deleted several mailboxes. I then went back to the Mac and deleted our email account. When I then reestablished our Mail account on the Mac, all of the remaining folders/mailboxes reappeared. WHEW!

No, that only showed or hid the sidebar. I'm calling them folders because the icon looks like folders, but they are actually called mailboxes within my email list. These subfolders all show up on my iPhone, but are gone from view from my Mac.