[SalesForce] How to customize the Lead Conversion Standard Email Notifications

There is no such field in API available as of now. Also you will not be able to achieve this with the help of workflows since for the TASK object even in workflow the email alert option is not available.

The probable approach according to me is to write down a trigger on the task object to send an email to the assigned user.

refer to this link for sending an email using apex

http://www.salesforce.com/us/developer/docs/apexcode/Content/apex_classes_email_outbound.htm

Refer to the Email section in the below link

http://www.salesforce.com/us/developer/docs/apexcode/Content/apex_gov_limits.htm

Config solution would be to create a simple workflow rule with

• condition = "every time a new record is created" (+ anything you have to distinguish the records like LeadSource = 'API' maybe?)
• email alert to the owner (you'd have to prepare an email template first)

Apex version could be to set a Task for the Owner with optional Email notification. Insert your Leads first, then for each create a list of Tasks with ParentId = lead.id and OwnerId = lead.OwnerId. The important part would be to not go with straightforward

insert tasks;

but use the DML Options

Database.DMLOptions dlo = new Database.DMLOptions();
dlo.EmailHeader.triggerUserEmail = true;
Database.insert(tasks, dlo);

I think the config version is cleaner (easier to maintain in future if you need to change the criteria or temporarily disable it).

You might also want to look into the Chatter Actions and Lead assignment rules (but assignment rules let you specify the notification only if you change the owner in same rule so potentially you'll need to move more logic from Apex to config before you can use it. And you'd still need to make an email template).