mail: mount mail data directory into sftp container

fixes #794

src/sftp.js

@@ -13,6 +13,7 @@ const apps = require('./apps.js'),
     debug = require('debug')('box:sftp'),
     hat = require('./hat.js'),
     infra = require('./infra_version.js'),
+    path = require('path'),
     paths = require('./paths.js'),
     safe = require('safetydance'),
     shell = require('./shell.js'),
@@ -66,6 +67,12 @@ async function rebuild(serviceConfig, options) {
         dataDirs.push({ hostDir: volume.hostPath, mountDir: `/mnt/${volume.id}` });
     }
 
+    // mail data dir
+    const stat2 = safe.fs.lstatSync(paths.BOX_DATA_DIR);
+    if (!stat2) throw new BoxError(BoxError.FS_ERROR, `Could not stat mail data dir: ${safe.error.message}`);
+    const resolvedBoxDataDir = stat2.isSymbolicLink() ? safe.fs.readlinkSync(paths.BOX_DATA_DIR) : paths.BOX_DATA_DIR;
+    dataDirs.push({ hostDir: path.join(resolvedBoxDataDir, 'mail'), mountDir: '/mnt/maildata' });
+
     const mounts = dataDirs.map(v => `-v "${v.hostDir}:${v.mountDir}"`).join(' ');
     const cmd = `docker run --restart=always -d --name="sftp" \
                 --hostname sftp \