It is possible to configure your Haileybury Society account to send from other email addresses that you own. This allows you to manage your various email accounts within Haileybury Society:

Webmail Accounts

Outgoing Mail
Set up multiple identities by clicking on:
OPTIONS > PERSONAL INFORMATION > EDIT ADVANCED IDENTITIES
Fill in the ADD NEW IDENTITY form. For example

Full Name: Bob Smith
E-Mail Address: bob@workaddress.com
Reply To: bob@workaddress.com

Click on the Save/Update button.

Now when you compose an email, you will have the option to send FROM this address. When replying to an email TO this particular address, the system will intelligently ensure that you respond using the appropriate address.

Incoming Mail
The above is especially useful if you route email from the other account to this account. You then avoid the hassle of having to check multiple accounts for multiple addresses. There are two ways to do this:

Forwarding - Set up forwarding from bob@workaddress.com to your Haileybury Society account.

POP FETCH - If your other account permits POP access you can set up Webmail to automatically download emails from the other account to Haileybury Society. Look under OPTIONS > POP3 FETCH MAIL. You will need to check your provider for the requisite server login information etc.

HOTMAIL - A fetch option for Hotmail is being developed!

If you set up the above, you will be able to manage all mail from multiple addresses within your Haileybury Society account.

Desktop Email Clients

Outlook
Outlook doesn"t seem to support multiple identities but you can simulate as much by creating a "dummy account" (eg a POP3 one that never checks mail). Set up everything the same, including the username/password and SMTP server but change the "email address" field to the one you want. When sending, you should be able to select the address to use to send from. This field is sometimes hidden. To show it, compose an email, click on VIEW and click "From Field".

Thunderbird
Click on TOOLS > ACCOUNT SETTINGS. Within the account settings, you should see a button called "Manage Identities" which will allow you to add other email addresses you use to send from. This allows per-identity signatures as well.

Mac Mail
Until recently we thought it impossible to configure multiple identities within Mac(Apple)Mail. However this article shows a clever hack to enable this feature. In short it says In your account configuration, enter a comma-separated list of addresses in the "Email Address" field..