One common problem people have is an incorrectly setup mail system. Here is a list of rules that must be followed:
1) hostname must not match any domain that is being used on the system. Example, if you have a domain called domain.com and you want to recieve mail on user@domain.com, you must *not* set your hostname to domain.com. We recommend using server.domain.com instead. You must make sure that you add the A record for server.domain.com so that it resolves.
2) The hostname must be in the /etc/virtual/domains file.
3) The hostname must *not* be in the /etc/virtual/domainowners file.
4) The hostname must resolve. If not, add the required A records to the dns zone such that it does.
5) The directory /etc/virtual/hostname must exist.. (eg: /etc/virtual/server.domain.com). It must not contain any files.
6) Any domains that you want to use for email (eg: domain.com) must be in both the /etc/virtual/domains file and the /etc/virtual/domainowners file. The directory /etc/virtual/domain.com must exist and the files /etc/virtual/domain.com/passwd and /etc/virtual/domain.com/aliases exist.
7) File permissions for virtual pop inboxes should be (not applicable with Dovecot/Maildir):

/var/spool/virtual/domain.com 770 username:mail
/var/spool/virtual/domain.com/* 660 username:mail

If you’ve made any changes to you /etc/exim.conf file and require a fresh copy, you can retrieve one with this guide:
http://help.directadmin.com/item.php?id=51
Ensure your hostname does not contain any upper case letters.
9) Make sure that your main server IP has a reverse lookup on it.

Overview

The Bandwidth Usage feature allows you to see the bandwidth usage for your site. It shows the current month’s bandwidth usage as well as your total bandwidth usage. This will include all HTTP (web) and POP (mail) bandwidth usage and may include FTP bandwidth usage if your system administrator has enabled FTP bandwidth logging.

Monthly Bandwidth Limit

Today

The next section shows the amount of bandwidth or traffic used on your web site for the current day. The “Traffic for Today” graph shows the amount of bandwidth or traffic on the following protocols:

• Http – Web site page bandwidth usage.
• Pop – Mail bandwidth usage.
• Imap – Mail bandwidth usage.
• Ftp – File Transfer Protocol or amount of file upload and download bandwidth usage.
• Smtp – Outgoing mail bandwidth usage.
• All – Total bandwidth usage for Http, Pop, Imap, Ftp, and Smtp.

This Year

The next section shows the amount of bandwidth or traffic used on your web site for the current year. The “Traffic for CURRENT_YEAR” graph shows the amount of bandwidth or traffic on the following protocols:

• Http – Web site page bandwidth usage.
• Pop – Mail bandwidth usage.
• Imap – Mail bandwidth usage.
• Ftp – File Transfer Protocol or amount of file upload and download bandwidth usage.
• Smtp – Outgoing mail bandwidth usage.
• All – Total bandwidth usage for Http, Pop, Imap, Ftp, and Smtp.

The last three sections shows the amount of bandwidth used for the last three months including the current month. The two months prior to the current month displays a “circle” graphic that says “Click to Show.” Click on the circle graphic to display the amount of bandwidth used as displayed on a pie chart.

SMTP Error 431 : The recipient’s mail server is experiencing a Disk Full error condition, or an Out of Memory (too many file handles) error condition (Microsoft Exchange).

Incoming search terms:

SMTP Status 220 : This is normally the first message you will get back from the server. It means the mail service is running (ie. your mail server is running). It will normally contain a welcome message and/or the title of the SMTP software and, sometimes, the version number of the mail server software. SMTP Reply 220 is effectively a “Hi There, I have just this second finished starting up – I am ready to go and at your command” informational message.

Incoming search terms:

SMTP Status 250 : The mail server has successfully delivered the message! This is the best SMTP reply (250) to receive – your message has been accepted and transmitted OK ! J Yippee. 250 is effectively a status code rather than an error code – there is no such thing as an SMTP error 250.

Incoming search terms: