How do you deal with Marketing VS Transactional emails to ensure delivery?'

If you are running a webinar in-house / to your own database (not 3rd party), how far in advance do you start promoting your webinar and how many invites do you send out? 

Currently, for our customer focused webinars we send two invites starting two weeks in advance. I'm curious to hear how others market webinars to their customer base.

------------------------------
Colette Chavalia
------------------------------