The most common reasons people stop receiving their lessons are:
(1) It gets caught in their spam filters
(2) Their email provider blocks the message as spam before it even gets to a spam filter
The first thing to always do when missing lessons is to check your spam / bulk folders. If you happen to use Gmail, also check and see if it landed in you 'Promotions' tab.
One thing you can often do that will help with the above issues is to reply to one of my messages. This usually signals to your email provider that I am a 'friendly' sender and will sometimes help get messages through to you successfully.
If you are missing lessons...
At this time, it is infeasible for us to re-send lessons. Fortunately, all of them are archived here to ensure that even if you miss an email, the lessons are always available to you.