You've just done it in your question.

Split the task into the individual steps and give estimates for each one. This will show that you've considered all the options and (hopefully) covered all eventualities.

If the timescales are too great you can then discuss what parts (e.g. e-mail confirmation) aren't need in this case with concrete data rather than just trying to cram a quart into a pint pot.

Do this often enough and you'll hopefully teach them that there's usually more to a development than meet the eye at first glance.

You've just done it in your question.

Split the task into the individual steps and give estimates for each one. This will show that you've considered all the options and (hopefully) covered all eventualities.

If the timescales are too great you can then discuss what parts (e.g. e-mail confirmation) aren't needed in this case with concrete data rather than just trying to cram a quart into a pint pot.

Do this often enough and you'll hopefully teach them that there's usually more to a development than meet the eye at first glance.