You can set it up in Paperless Office and printing the statements and selecting Electronic Delivery will send them out.  This would require you obtain the email address for each customer and enter it in the Paperless Option settings for the customer

Exactly as BigLouie indicates, this is available as a regular Sage 100 feature, but hidden in the AR - Period End menu.

The biggest issue is that the email address that is part of customer maintenance is not the email address that we send statements to for some of our customers.  Is there a way to maybe set up a user defined field that paperless office could use for sending out statements?   Because right now, the email address is usually the buyer's email address that we confirm orders back to.

Yes that is an issue because right now Sage seems to think that company would use a single email address for every situation be it statements or sales orders or invoices.  You other option would be Sage Alerts and Work Flow but that would require building a statement from scratch in Crystal.

In Customer Maintenance, Paperless Office Delivery Options, when you select Document=A/R Statement, you have the choice of using the Customer E-mail Address and/or entering any number of Contact Codes (first grid) or any number of specific E-mail Addresses (second grid) for the PDF to be sent to.  Just don't select the check box for Use Customer E-mail Address and then enter the specific E-mail Address the statement should be sent to in the second grid.

To answer your question about adding a UDF and have that used when sending documents, no, the standard logic in Sage 100 would not support that.

Steve beat me to it!  Each document type has its own email settings, which are flexible.  v2019 adds the ability to cc the salesperson emails with a checkbox.

I find contact codes are better than "Additional e-mail addresses" which are more difficult to maintain in bulk.