I quite often refer to my old email as “the mail sent on 2011-12-31 23:59” or “the mail received on 2011-12-31”.
For this purpose there would be nice to have a button on the right side of the “Sent:…” row of the email header. The button would copy the sending/receiving timestamp to the clipboard in a configurable format.
Maybe a right-click option would be easier to implement. If I right-click on a timestramp now the “Select all” is available and “Copy” is inactive. Besides these options a “Copy all in format YYYY-MM-DD hh:mm:ss” would be nice to have.
The format (more formats?) should be configured in Tools => Settings => Appearance => Mail.