Does a triple divorce occur if the husband sends his wife a message via mobile phone – by way of intimidation – stating that if she performs a certain act, she is triply divorced, knowing that this is the third divorce, and the wife performed this act out of forgetfulness and then remembered?

Writing the divorce is a form of an implicit statement (kinayah), and it does not effect a divorce unless the husband intends it. This is the view of the majority of jurists. Therefore, your wife has not been divorced by what you have mentioned.

You must avoid swearing by divorce in the future, as it is an oath of the transgressors and it is not permissible to swear by it.