Just a theory, but some clients support external stylesheets which can be changed manually or automatically. With this in mind maybe it's possible to change the css file based on the time of day like for example the live twitter feed in email form Litmus https://litmus.com/blog/how-to-code-a-live-dynamic-twitter-feed-in-html-email
Hi Veronica, Do you mean hiding content on mobile clients that doesn't support media queries? If so, you could look into hiding by default through inline styles and then show on desktop by using embedded stylesheets, min-width media queries, the use of the [owa] hack etc. Only a couple of exotic email clients don't support embedded stylesheets these days.
Don't know for Microsoft based services. Maybe it's based on a combination of reputation (DKIM, SPF etc.) and your contactlist. You could try creating a microsoft account with your sender email address, upload an avatar and add this account to your contactlist.
I've read somewhere that you can set the avatar icon in Gravatar on the from email address of your email campaign with your logo. It’ll then show in your receivers inbox next to your name in Thunderbird, Postbox and Airmail.
I did some basic testing a couple of months ago and have a list of clients that seem to support external stylesheets: https://litmus.com/community/discussions/6405-external-stylesheet-support