The mail settings in WHMCS will cover some technical considerations, such as which “mail type” to use, and they will also cover some aesthetic considerations like email signatures, CSS styles, header and footer content, and more.

1. Login to your WHMCS Admin
2. 

   Hover over Setup and choose General Settings
3. 

   Choose the Mail tab
4. Fill in the settings:
   

   Mail Type:	Select the mail type you want to use to send emails
   Mail Encoding:	Select from the dropdown
   SMTP Port:	The default port your mail server uses
   SMTP Host:	Enter in the SMTP Host (typically your domain)
   SMTP Username:	Enter the username to send emails from
   SMTP Password:	Enter the SMTP password
   SMTP SSL Type:	Select the SSL type radio button
   Global Email Signature:	Enter an email signature in the field
   Global Email CSS Styling:	Add any global CSS you wish to use in emails
   Client Email Header Content:	Any text you enter here will be prefixed to the top of all client email templates sent out by the system. HTML is accepted.
   Client Email Footer Content:	Any text you enter here will be added to the bottom of all client email templates sent out by the system. HTML is accepted.
   System Emails From Name:	Enter the name you wish to display on emails
   System Emails From Email:	Enter an email address to send from
   BCC Messages:	If you want copies of all emails sent by the system sent to an address of yours enter the address here. You may enter multiple addresses seperated by a comma (,)
   Presales Form Destination:	Select a department OR enter an email below
   Presales Contact Form Email:	Enter the email address for your presales email to be sent to

5. 

   Click Save Changes

Now that you have gone through the Mail options you are ready to proceed to the Support tab.

destination source:https://www.inmotionhosting.com/support/product-guides/reseller-hosting/how-to-configure-mail-settings-in-whmcs