Respected Sir/ Madam,
This is in regard to the meeting scheduled for __/__/____ (date) at time __:__ (mention time) for the ________ (mention purpose).
I write this email with a sense of apology, as I would like to inform you that I will not be able to attend the meeting on the said date. Respected, the reason behind the same is _____________ (mention reason for postponing the meeting).
Therefore, I write this email in order to request you to kindly reschedule the meeting and postpone it to __/__/____ (date). I shall be highly obliged for your kind support.
____________ (Mention name),
____________ (Company details)