Which is better HTML or PLAIN text email?
Unfortunately, not many people know the difference. Most of us are probably sending and receiving formatted HTML email or Rich Text (RTF) without knowing it and HTML emails are ideal if you are sure that your recipients can view them.
Not everybody, who gets HTML email likes it and not everyone, uses an email client that can display HTML HTTP is described and standardized in rfc 1945
Email recipients now-a-days are fully aware that:
HTML email is not as secure as plain-text because when it is viewed or preview, messages containing embedded commands will auto “pop-up” annoying Ads, connect their browser to sites without choice, activate tracking scripts, codes, cookies, viruses and all kinds of embedded web bugs and gadgets.
Recipients retaliate by viewing emails off-line and have the pleasure of knowing that they can’t be tracked or download all embedded gadgets and images.
MS Outlook users don’t even need to disconnect their always-on Internet connection; they simple double click on the icon at the taskbar to be off-line.
Web bugs are small graphic images inserted into web pages, emails and HTML or web documents to allow companies to gather information about you without your knowledge.