If you have a cPanel server and you get ‘SMTP Error 451′ when sending e-mails via either webmail or a straight up client like Outlook or Thunderbird, it’s likely going to be an issue with the ‘/etc/localdomains’ file.
SMTP Reply Codes
This is a great website for SMTP reply codes. Useful for debugging issues or understand what a remote MTA is telling you via telnet:
http://www.greenend.org.uk/rjk/tech/smtpreplies.html
cPanel: Protection From Brute Force
If you’re trying to FTP to your server and you’re being kicked off before you get a chance to do anything; or if you’re trying to send mail and can’t, it’s possible someone is attacking your server and trying to brute force its way in.
Plesk FTP IP Connection Limit
Plesk uses, by default anyway, the ProFTPd FTP service. This service is wrapped by the xinetd service, which handles incoming connections and spawns a ProFTPd process to handle it. The number of processes that can spawn is unlimited, but the number of connections per IP is limited to ten.
Plesk Domain Limitation
In recent days I have been presented with an odd issue in Plesk. When a client of mine was hitting the 300+ domains mark, applications such as Horde stopped working (‘Zero length reply’ errors and segmentation faults in the error logs). The reason for this is beyond the scope of this blog (I’m here to provide fixes, not indepth analysis), but it involves open file descriptors and piped logging.
All Plesk FTP Accounts with Domains
Grabbing all the user name and password combinations from Plesk is easy, but getting the domains along with them is a bit more complex.
Plesk Administrator Password from the CLI
In the event you need to update the Plesk password via the CLI, the following will help you out:
/usr/local/psa/bin/init_conf -u -passwd <new_password>
The original Plesk KB article can be found here: http://kb.parallels.com/346
Migrating Exclusive IPs in Plesk
The Plesk Migration Manager (PMM) is designed to make migrating data an easy task. It does this by offering you the chance to migrate from one Plesk server to another Plesk server; all data such as e-mails and websites are copied. There is a pitfall all users get caught by, however…
Showing Hidden Files in cPanel
You need to check a sneaky box that some people miss when they open the file manager. Check out this screenshot:
Show Hidden Files
Provided the ‘Show Hidden Files (dotfiles).’ check box has been marked, you will see ‘.dotfiles’ (hidden files) in the file manager.
MySQL Breaking with cPanel Update
cPanel updates automatically, which is fine and dandy, except when it breaks your running MySQL implementation and prevents it from restarting, rendering all your websites off-line.