Hi @Richard_Wein,
The only way to send emails from outside of HubSpot is with the transactional add-on. We offer both an SMTP and Single Send Option. I appreciate that there is a cost factor invovled with this of course and it may not necessarily make sense given the size of the project.
@jgalloways solution is also another one I’ve seen used - programmatically enrolling contacts into workflows and using the “Send external email” action. This would only be available if you are a Marketing Professional customer and does not support attachments Generally speaking marketing emails with attachments have implications regarding spam.
Whilst I appreciate this isn’t the ideal answer I just wanted to confirm it for you from a HubSpot perspective.
Regards,
Jack