Do you use MBS Plugin?
There you have much more control about sending emails.
Multiple attachments from container or file, correct text encoding, HTML emails with inline graphics and secure connection to SMTP server.
I gather the plugin will need to be on any computer using the database. As this is quite flexible, I need to keep it with filemaker script steps if possible. At worst I can script to create the file to be sent and then send them individually. Since it may mean clicking the send button no more than 20 times (the number of club secretaries involved), I guess the users will find it acceptable, given the time the database saves elsewhere.