Open the Mozilla mail client, then go to ‘Edit’-> ‘Mail & Newsgroups Account Settings’ as shown below in Figure 1.

Figure 1

Step 2:

When the dialog box appears, select the ‘Outgoing Server (SMTP)’ option on the left hand side.  Ensure that the ‘Server Name’ text box contains the outgoing mail server for the account in question (smtp.skybest.com).  Select the checkbox labeled ‘Use name and password’, and then enter the full email address of the user in the ‘User Name’ field.  See Below in Figure 2.  Hit ‘Ok’ to apply the settings.

Figure 2