Hi Cathy, please visit the customer portal knowledgebase.  For quick reference, here is the article on "How to configure document transmittal".

1. Login to the Sage 500 ERP application
2. Expand Common Information, Maintenance, CI Setup double-click Set Up CI Options.
3. Under E-Mail, select the transport option used with Sage 500 ERP. Specify the Exchange server, if applicable.
   1. If using Microsoft Exchange, the Outlook 98 or 2000 client is needed.
   2. If using SMTP, Windows 2000 and an SMTP-compatible e-mail client is needed.
      Note: Outlook Express is not a supported e-mail service for Document Transmittal. CDO.dll Version 2.1 or greater is required, and Outlook Express does not include this component.
4. Under Common Information, Maintenance, CI Setup double-click Set Up Document Transmittal.
5. Set the following options for e-mail messages:
   1. Carbon copy (cc) and blind carbon copy (bcc) recipient e-mail addresses
   2. Text that appears in the subject and body text
   3. E-mail options for Microsoft Exchange or SMTP
   4. A return address if using SMTP
6. To specify whether a customer or vendor receives documents by e-mail:
   1. Start Accounts Receivable, Maintenance, Maintain Customers or Accounts Payable, Maintenance,Maintain Vendors, and select the applicable vendor record.
   2. Verify that the primary contact information includes a valid e-mail address
   3. Click the Doc Transmittal button to specify the applicable information.
      1. Select the Transaction type(Invoice, Credit Memo, Customer Statement etc...)
      2. Select E-mail
      3. Select desired E-mail Format 
      4. Click Checkmark to save
7. If using Windows 2000 and SMTP, verify that the service Simple Mail Transport Protocol (SMTP) is installed and running on the system.

Note: The e-mail address used by Document Transmittal is stored in the tciContact.EmailAddr field. DocDistributionUtils.dll and EmailUtils.dll are the two common .dll files used for the document transmittal process. The EmailAddr value is selected within DocDistributionUtils.dll.