Is it obligatory to begin all letters and official correspondence with praise to Allah and prayers upon the Prophet, even if addressed to managers or officials and not religious in nature, and can this be considered a form of indirect دعوت (propagation)?

It is recommended to begin important letters, books, and correspondences, whether religious or worldly, with the Basmalah and the remembrance of Allah, following the example of the Holy Qur’an and the practice of the Prophet, peace and blessings be upon him. This recommendation is further emphasized if it includes praise and glorification of Allah and prayers upon His Prophet, especially if there is a benefit or need that calls for it.