I ran into a problem today and thought I'd post the solution here in case anyone else runs into it. I am migrating customers from my old server with no control panel, but with vchkpasswd to Plesk. I wrote a script that takes the vpasswd file and assorted .qmail files and generates a script that calls mail.sh to migrate account information. This morning it migrated an email account that had an alias which contained an underscore. The old system replaced _ with :, so it generated the following mail.sh parameter: -aliases add:first:last The script ran just fine, but this account wouldn't receive email. All other accounts in the domain worked, and some aliases to this account worked, but not the regular name for it. It turns out that in /var/qmail/users/assign the : was written unchanged into the user ID field, and this caused mail deliver failures with the error "Not_allowed_to_perform_deliveries_as_root". I guess when the parser failed it gave a zero for the user's UID. I updated my script that generates the configuration to replace : with _ and manually updated the user with the problem and now all is well. I hope this helps someone!