To get to my point, adding a link to web version of your email is good practice and does add value for both the sender and the recipient but there is one aspect of the communication process that is being overlooked.
Lots of people first see they have a new email through a notification system like the one built into Outlook. When this notification pops up on my screen, it shows me the subject of the email, and also the opening text which acts as a teaser to get me to click on it. In so many cases these days, the opening text I get is – Does this email look weird to you?