Dear ________ (name),
Greetings of the day,
I, __________ (name) write this email to inform you that I am going on for maternity leave from __/__/____ (date) onwards. Most happily, I am glad to inform you that the expected date of delivery is __/__/_____ (date).
In case you wish to contact me, please do not hesitate. You may reach me at __________ (contact details). I will be available to take calls.
Regards,
___________ (Name),
___________ (Contact details)