adding note about viewport size

[M-J-Robbins]

Added a note based on this conversation here https://emailgeeks.slack.com/archives/C1Z733K1P/p1717319677837359?thread_ts=1717175491.511369&cid=C1Z733K1P

I've not been able to test fastmail, protonmail or SFR webmail clients.

[husseinalhammad]

I don't think "buggy" is the best description here. It works exactly as expected on the webpage as a whole. Perhaps something more specific along the lines of:

The HTML of the email message is embedded directly on the webmail (not in an <iframe>) and does not fill the full viewport's width. In this case, the vw values are relevant to the viewport (browser window) not the email message.

Perhaps it needs to be even more detailed. A lot of webmail clients allow you to open the message on a separate window. In that case, the email message width equals the full viewport width.

[M-J-Robbins]

@husseinalhammad yeah that sounds much better. How about "may not fill the full viewport's width" instead of "does not fill the full viewport's width" to account for opening in a new window.

The HTML of the email message is embedded directly on the webmail (not in an