Google "filemaker bulk mail"
#1 SeedCode Calendar Complete will let you email or print letters to found sets
#2 Email Merge is a program for Macintosh
Look into the Send Mail script step. If you have a contacts table then you can collect the email addresses across the found set.
Also I probably would recommend breaking then addresses into smaller groups ( maybe like 50 at at time ) not to overload the email server or the SMTP function.