You need to concentrate on the e-mail sending side of things. Notes (from R5 upwards) has been able to handle external e-mail (including HTML and attachments) as part of the default mail gateway.

Use a minimal test rig to work with various Mail:: modules. Configure a Domino server to run the SMTP task and then use this as your SMTP gateway. You can deliver mail to a mailbox on the same server and examine it immediately.

I have used Mail::Sender with a Domino environment in order to send status messages. I haven't worked with attachments but the docs say that it can.