There are no build tests for webmail
There aren't currently any tests to ensure webmail (ie: roundcube) is functional.
This is less of an issue at the moment as IMAP is tested, so this can be put off for now.
We should however create a test to ensure webmail can be logged into (via cURLing the local site, etc.
To upload designs, you'll need to enable LFS and have an admin enable hashed storage. More information