If you use a hosted email provider or Outlook 365 then you will need to setup SMTP as your email method. When you use SMTP the IT department will need to provide you with the server name, port and authentication to send through the mail server. Once this information is entered you can test the mail server by selecting Verify SMTP on the Email Suite Setup window (HR and Payroll > Setup > Payroll > Email Suite).
The key difference when using SMTP verses Outlook is the emails go directly though the server thus most of the time you cannot go to your sent items folder and see that the email were sent. If you would like to see the email sent or have a copy of the email, you can setup the system to blind carbon copy your email address or a general payroll email address on the Email Suite Setup window. Then you will receive a copy of all the sent emails.
An exception to this is if the user can login to the mail server account they are using to send emails. For example, Gmail users send via their Gmail account. Since the Gmail account is the server account they use to authenticate you can see the emails in the Gmail sent items folder.
If you have an install of the Outlook client then you can use the Outlook sending method and install the Email Suite Outlook Addin. The emails will send directly from the Outlook Account available on the machine that processes the emails. With this option, you do not have to setup the SMTP mail server settings. After you process the emails, your Outlook client will send them. One advantage to using the Outlook Addin is you can go to your sent items folder and verify all the PDF files were been sent. The disadvantage is Outlook and the Outlook Addin is required on the machine that processes the emails. If you use a terminal server then Outlook needs to be installed on the server. Keep in mind, an Outlook user can use SMTP if they would prefer that sending method.