You can try to add style="margin: 0 auto" to the outer table with a width of 640 or you can create a table with a width of 100% around the current outer table like this:
<table width="100%" border="0" cellspacing="0" cellpadding="0">
<td align="center" valign="top">
<table width="640" border="0" cellspacing="0" cellpadding="0" align="center">
This approach from Mark Robbins works as well:
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.