Why are some of my contacts receiving plain text versions of my campaigns?

There could be many reasons for this. The first thing to check is the delivery format of the contact and/or group. It should be set to HTML.

Second, the contact's individual device (e.g. computer, mobile phone, etc.) where they are receiving the mail and the email client they are using to read the mail must be configured properly to receive HTML messages. Certain mobile devices, for instance, may only display the plain text version.

Third, the recipient's mail server may display the plain text version either because the individual recipient turned HTML off for incoming emails, or a setting on their company email system is causing the plain text version to be displayed.

If the contact and group are set to HTML delivery format, and they are not viewing the message on a mobile device that can only display plain text, we would recommend asking the recipient to contact their IT department to inquire about why they are receiving the email messages as plain text. Their IT department may need to whitelist the IP addresses used for sending campaigns from our system and/or modify another setting that could be affecting how the incoming mail is displaying.