Autoresponder for filling out profile
I've managed to solve problems like this by generating custom activities, and then creating scheduled reminders which trigger on these activities.  This is better than using sendmail directly, because the email more easily managed from the front end.  For more information on automated reminders, see the docs.

For generating activities on forms submits, you could use hook_civicrm_postProcess to trap the form submit.  For generating activities on new contact creation, you could use hook_civicrm_post.  For more information on hooks, see the docs.

From within the hooks, you can create new activities like so:

civicrm_api3('Activity', 'create', array(
    'source_contact_id' =&gt; $id,
    'activity_type_id' =&gt; $activity_type_id,
    'subject' =&gt; "Participant $id Status Changed to $pstatus",
    'status_id' =&gt; 2,
    'assignee_id' =&gt; $member_org_poc_id,
    'details' =&gt; "Participant #{$id} Status Changed to $pstatus",
));