If you are concerned about some email content then you can choose to view some or all emails in a plain text only format. Normally emails are displayed as formatted HTML with images.

You can change the text display format in the App Settings - Security section. View emails as plain text View
You can choose which emails will show plain text instead of full formatted HTML and images:
Always This will always show emails with a plain text messages
Unknown Sender Emails from people you don't know will be displayed as plain text. This is the list of 'Known Senders'. View
Unless S/MIME Signed Emails without a valid S/MIME signature be displayed as plain text.

When you are viewing an email in text format you can will see a notice message at the top of the email. Tap on 'Show' to show the email message as formatted HTML with images.

You can see a list of remote images and web links for an email in the email details screen before you view the formatted content. View