Also, this may be the problem.
Previously in Notes R4.x, users used to be able to send to other Notes users across the internet by enabling the delivery option "Sending this Notes document to other Notes mail user(s) through the Internet" which allowed that
message to retain the Notes formatting that is usually stripped away by sending the message through the SMTP MTA. In R5, while this option is still available to the client, the SMTP server function currently does not convert back to Notes format messages that are sent with this option flagged.
I have a copy of a database which will convert it for you.