Why does asterisk build with voicemail IMAP support
As far as I know, all other vendors ship asterisk without voicemail-IMAP support, and provide an 'asterisk-voicemail-imap' package to provide this functionality. Since only one voicemail option is supported out of the box, it is currently impossible to configure asterisk to use the filesystem for voicemail storage
I found this ticket from several years ago mentioning IMAP support, but at that time, the request was for a separate package (as other distros do): #4840 (closed)
To upload designs, you'll need to enable LFS and have admin enable hashed storage. More information