Answer:
The Deputy Prime Minister and all other Ministers of the Cabinet are styled: ‘Honourable’
For example:
Deputy Prime Minister & Minister of ________________________
Ministry of ______________________
Opening Salutation:
‘Dear Deputy Prime Minister/Mr Minister/Sir
……………………………………………………………..
Yours faithfully (formal usage)
Yours sincerely (semi-formal usage)
Signature’
If the Minister is also a Member of the Senate, he/she should be formally styled as ‘Senator the Honourable’:
Senator the Honourable Kamina Johnson-Smith
Minister of Foreign Affairs and Foreign Trade
Opening Salutation:
‘Dear Senator Johnson-Smith/Hon. Minister/Madam Minister
………………………………………..
Yours faithfully,
Signature’
((Hope it helped))