Hi Luciana
You can achieve it by using a Java Multi Mapping.
Basically, in your Java mapping, you read all your attachments that you receive from the mail sender, then you create multiple output messages. The file receiver adapter will generate the separate files from the multi message.
Apart from the Wiki link above, you can refer to Praveen Gujjeti's following blogs on how to read the attachments and how to form the multi message.
Attachments zipping during Mapping
N:1 & N:M mappings not possible without BPM... Any more !!!!!!!!!!
Do remember to set the "Read Attachment" checkbox when you include the Java Mapping in your Operation Mapping.
Rgds
Eng Swee