The two most common issues here are Authentication and port blocking.
First, check to see that you have the My server requires authentication box checked on the Servers tab of the account properties in Outlook or Outlook Express. Other mail clients should have a similar setting.
Second, many ISP's block port 25 (SMTP) and require that you use thier SMTP server for sending email.
This problem can be identified by testing the following command via command line (START-->RUN--> type command): telnet mail.yourdomain.com 25
A failure on this test indicates that, either you are behind a firewall that has this port blocked, or your ISP is blocking the port. In this case, you will need to contact your ISP to resolve this.

In order to setup a custom MX record, simply turn off the Mail service in that account, and this will remove the Built-In MX record, allowing you to add a custom MX record.

Every email that is sent to a client's pop3 mailbox is first checked with SpamCops SPAM list.
If the sender is on their list, the SPAM email is dropped and never makes it to the client's mailbox.
This automated SPAM protection tool makes protecting yourself from SPAM an easy task. The greatest feature besides not getting SPAM is there are no setups required in the client's email software (Outlook, Eudora, Netscape, Ect) or web mail.
Also you have the ability to configure general and antispam Qmail settings directly from the admin H-Sphere web interface

Several things can cause a 'timeout' when sending attachments: connectivity issues, slow Internet connections (Dial-up), attachemnts over 1 MB.
When sending large messages (typically 1MB or more), it is possible that your connection to the server may timeout before completing the sending process.
To resolve this, try increasing the connection timeout setting in your email client. In Outlook Express, this setting is located on the 'Servers' tab of the account 'Properties' for the email account in question.

Look like you're exceeding a timeout somewhere. The receiving server is taking too to respond with 250 after DATA and the client disconnects, trying it again later.... Please ticket us to check the server load.

Here you'll find all the information you need to setup your email accounts.