How to send email invite user fill in webform automatically? I'm using drupal 7, and had a seminar questionnaire form created using webform.

I would like to invite seminar attendee to fill in this questionnaire after they attend the seminar, by sending them email with link to the questionnaire.

Rather than manually open my email client and retyping the same invitation template for every seminar, is there anyway I can have this?


A standard template of email invitation content with webform link
Admin only need to type in different email address of each seminar
Email will automatically sent to address entered
Attendee do not need token or account to fill in the form 
It's similar to google form share this form / invite through email function


Is there any module to do this? Or I need to use with other modules such as Rules?
There are a handful of different modules that can let you do bulk emailing (e.g. VBO, Mass Contact, Email Campaigns, etc.), but using Drupal as a batch email client I think only make sense in the context of:


Having regularly visiting user base, with pre-existing accounts.
Needing to contact a relatively small number of people (e.g. hundreds, or very low-thousands). 


Your 4th requirement suggests that you'll be supplying any number arbitrary emails for the sake of feedback/lead gathering.

In lieu of a module or Rules (which only make sense in the context of some workflow built into the site), I'd suggest some 3rd-party email service (e.g. Constant Contact, MailChimp, etc.) to accomplish items #1-4.
Any decent 3rd party email service should give you a templating system with substitutable tokens that will let you customize your webform link if you need it to have pre-filled data (e.g. email, name, attended seminar, etc.) and a means to bulk submit email/contact info.  

As far as item #5, there's a number of different way to accomplish this. One way is the Forward module which provides a share via email link/form for any node type.