Need API to insert record choosing multiple options and tigger email.

Need API to insert record choosing multiple options and tigger email.

I have a Multi select lookup field "Source" (Custom Field) in Leads module.
I want to Insert records in leads with more than one option selected in "Source" field.

On inserting the lead from API, there should be an email workflow triggered to send mails to all the sources.

1- I have created a email work flow but I cannot send mail to all the sources.(works for single select lookup field, but no option for multi select field)
2- There is no document on how to insert record in lead module via API by choosing multiple options in "Source".

Is this a limitation?