Mrs Bourne, 60, wrote the email after stepson Freddie took Heidi Withers to meet the family.
The message slammed her "lack of grace" and branded her "an ideal candidate for the Ladette to Lady television series" a show that takes drunks and turns them into ladys.
Stunned Heidi, a 29-year-old PA, forwarded it to pals. They sent it to others - and the message was soon on a host of websites and being read around the world.
Mrs Bourne has since been labeled the mother in law from hell and various other unflattering things however she also has many supporters who say she is correct in what she did.
So what do you think after reading the mail below
Bride to be Heidi Withers and Freddie Bourne the son of Mrs Bourne
The E-mail in it's entirety
From: Carolyn Bourne
To: Heidi Withers
Subject: Your lack of manners
It is high time someone explained to you about good manners. Yours are obvious by their absence and I feel sorry for you.
Unfortunately for Freddie, he has fallen in love with you and Freddie being Freddie, I gather it is not easy to reason with him or yet encourage him to consider how he might be able to help you.
It may just be possible to get through to you though. I do hope so.
Your behaviour on your visit to Devon during April was staggering in its uncouthness and lack of grace.
Unfortunately, this was not the first example of bad manners I have experienced from you.
If you want to be accepted by the wider Bourne family I suggest you take some guidance from experts with utmost haste.
There are plenty of finishing schools around. You would be an ideal candidate for the Ladette to Lady television series.
Please, for your own good, for Freddie's sake and for your future involvement with the Bourne family, do something as soon as possible.
Here are a few examples of your lack of manners:
When you are a guest in another's house, you do not declare what you will and will not eat - unless you are positively allergic to something.
You do not remark that you do not have enough food.
You do not start before everyone else.
You do not take additional helpings without being invited to by your host.
When a guest in another's house, you do not lie in bed until late morning in households that rise early - you fall in line with house norms.
You should never ever insult the family you are about to join at any time and most definitely not in public. I gather you passed this off as a joke but the reaction in the pub was one of shock, not laughter.
I have no idea whether you wrote to thank [your future sister-in-law] for the weekend but you should have hand-written a card to her.
You should have hand-written a card to me. You have never written to thank me when you have stayed at Houndspool.
[Your future sister-in-law] has quite the most exquisite manners of anyone I have ever come across. You would do well to follow her example.
You regularly draw attention to yourself. Perhaps you should ask yourself why.
It is tragic that you have diabetes. However, you aren't the only young person in the world who is a diabetic.
I know quite a few young people who have this condition, one of whom is getting married in June. I have never heard her discuss her condition.
She quietly gets on with it. She doesn't like being diabetic. Who would? You do not need to regale everyone with the details of your condition or use it as an excuse to draw attention to yourself. It is vulgar.
As a diabetic of long standing you must be acutely aware of the need to prepare yourself for extraordinary eventualities, the walk to Mothecombe beach being an example.
You are experienced enough to have prepared yourself appropriately.
No-one gets married in a castle unless they own it. It is brash, celebrity style behaviour.
I understand your parents are unable to contribute very much towards the cost of your wedding. (There is nothing wrong with that except that convention is such that one might presume they would have saved over the years for their daughters' marriages.)
If this is the case, it would be most ladylike and gracious to lower your sights and have a modest wedding as befits both your incomes.
One could be accused of thinking that Heidi Withers must be patting herself on the back for having caught a most eligible young man. I pity Freddie.