I have lot of files and I want to send different messages to different mails with a single mail connector.
You should be able to do something similar to this:
Basically what I have here is just a branch that will send three emails, the content etc. is determined in the Message shapes. In my example I am using the same Email Connection and the same Email Oepration, here you could of course change the operations to be individual if for example you have different requirements on the attachment structure etc.
I am not sure if you mean by "single mail connector" that you do not want it in this manner, if not I beleive you should be able to create some sort of for loop in Boomi but this sounds quite complex if this example is not sufficient for you.
This can of course (I assume) be handled using one connector as well, if the Set Properties shapes are conencted to a single Email connector, but then you will loose the flexibility of handling attachments etc. in seperate manners.
Retrieving data ...