When is the maher (dowry) payable and when is it not?

Fatwa, posted 4.22.2010, from United Kingdom, in:
Fatwa Question or Essay Title: 
When is the maher (dowry) payable and when is it not?
Websites and Institutions: 
Sharia Council of the United Kingdom, (London)

Maher is prescribed to be a compulsory gift from the husband to his wife. The husband must pay the agreed amount of maher unless relinquished by his wife. Payment of the maher may be prompt or deferred as is agreed between the parties. However, if the husband dies or the wife is given divorce by the husband, the maher becomes payable at once. If the wife seeks the divorce from the husband in exchange for her relinquishing the whole or part of the maher and the husband divorces her on this, then it is not payable.

Some other circumstances where Maher does not need to be paid are:

    1.If separation takes place between husband and wife from husband's side on a Sharia basis like provision of choice on attaining manhood. Alternatively if someone married him other than his father or grandfather and the separation happened before consummation or communion (husband and wife were in a separate room where conjugation could have taken place).

    2.If separation caused by the wife before consummation or communion for whatever reason like she had the provision of attaining puberty, or was given into marriage by someone other than her father or grandfather. It could also be the case if she apostates or commits conjugal relations with the father or the son of the husband.

    3.If the wife relinquishes willingly her right of Maher or makes it a gift towards her husband while she is in a sound state of mind and is mature.

    4.If marriage between the husband and wife was of an incorrect manner (for example, if the husband was taking the woman for his fifth wife) and the marriage dissolved before consummation or communion.