Wordpress Contact form 7 date format incorrect
From the documentation:
Format Date Value in Mail
As previously explained, if a value is specified in a date field, the value must be in YYYY-MM-DD format (e.g. 2013-04-08). When the value is inserted into mail template, the date format keeps by default. To change the format in mail, you can use a variant of mail-tag notation
[_format_{field name} "{date format}"].
So, to change the format for mail, you need to give a date format to your mail tag. This is separate from any formatting you apply to form fields.
Note also that you're meant to replace "your-date" in the examples with the name of your actual field, so for example, your mail tag should be:
[_format_date-387 "D, d M y"]