I'm looking for some stats on what % of users block HTML emails or block images (as this is a different thing).
Are HTML emails block by email clients because they may contain "suspect/phishers" code?
Also if you are doing a media release what are the advantages of HTML other than branding / Tracking over say a txt email.
I think it's safe that no email clients block emails because they have a HTML version, but some spam filters will react differently to HTML/Text/HTML + Text.
Branding and tracking are the 2 advantages of using HTML over plain text, but if these aren't important to you then going with plain text is probably the best option because it's going to be the quickest for you to put together.
We personally prefer to have the branding in tracking in our newsletters, so we always sent as HTML + Text.