I'm using "[DOMAIN]_" as "user prefix" in ISPConfig. I've been having troubles when a client register a very log domain name, because ISPConfig limits the entry field lenght in then "create user" page. I think there's no such limit in linux's usernames, I can manually create longer names than those allowed at ispconfig panel. I think it's a bug in ISPConfig. Meanwhile, I'm thinking in reverting prefix to default. Is there any problem in having some users with one prefix and some other with another in the same domain? Thank you very much!
Its not a bug in ISPConfig, some linux distributions that ISPConfig supports limit the username length, thats why we have to limit it too. No.
But if its important to you to have longer usernames, you can try to change the regular expression that validates the usernames in the file /home/admispconfig/ispconfig/lib/plugins/isp_username,plugin.php
