While it is possible to support email attachments by writing a specialized service task, it would be much more convenient when activitis MailActivityBehavior would support attachments out of the box.
I propose to add one new property to the mail task configuration: attachments
This can either be a java.util.File, a String, or a javax.activation.DataSource, or an array of one of these objects.
A file is just attached as is, with the name of the file as name of the attachment, and a String is interpreted as path to a file.
In case of a DataSource, the name attribute of the data source is used as name of the attachement.
I have prepared a patch for this (including tests and user manual), but I am of course open for different suggestions for this interface.
(The real work is done in the 3rd patch - the first increases the commons-email version and the second is a fully optional minor cleanup.)