sendmail via subform event

sendmail via subform event

I have two forms: Projects and Tasks.  Tasks is referenced via a subform within the Projects form, so users will only interact with the Projects form, and won't touch the Tasks form directly. 
I want to send an email when new tasks are added via the Tasks subform in the Projects form. 
I am using the sendmail function on the Projects > Tasks (subform field) > On Add Row event, without success.  I suspect the problem is that OnAddRow executes the script as soon as a new row is created, but for my purposes, I need an event that waits for users to finish inputing data into the new row before sending the message. 
Am I right about this?  Is there a way to do this from a subform?  The sendmail script I'm using works fine if I put it under Tasks > OnAdd > OnSuccess, but that requires users to interact directly with the Tasks form, and that won't work for me.
Any help is much appreciated.