In its original form, e-mail could only contained unformatted text. Subsequent to the development of e-mail, people found ways to add attachments to it. Attachments are actually a long block of what looks like random text, between a specially formatted header and footer. When attachments first became possible, you had to copy the random looking attachment text, from between the header and footer, into other software to convert the random looking text back into the attached file. Modern e-mail client programs, like Microsoft Outlook and Mac Mail, do the conversion automatically and create an attachment icon.
These days we are all used to being able to use formatted text (bold, underlining, colours etc.), in our e-mail. In order for the text only e-mail system to process these formatted e-mails, they are also converted into attachments. An unformatted version sent too, so that people using simple e-mail programs can still read them. E-mail client programs, usually show us the formatted text automatically, hide the plain text and hide the attachment that contained the formatted text.
There are subtle differences in the ways e-mail client programs handle all (e.g. attached PDF vs formatted e-mail) of these attachments, that can lead to confidential unformatted e-mail text being passed on. Here are some methods to prevent this from happening.
If you are a Mac mail user, corresponding with users of other e-mail clients, stick with plain text e-mail.
In Apple Mail, go to the menu Edit > Attachments
Make sure the following settings are checked:
- Always Send Windows-Friendly Attachments
- Always Insert Attachments at End of Message
Use the menu Mail > Preferences and go to the Composing section. Set the Message Format to “Plain Text”.
Remove the unformatted text attachment, when forwarding e-mail.
When forwarding e-mail, remove the last ATT0000x.htm attachment. It is also identifiable because it will be a different size to the rest of the ATT0000x.htm files.
Unfortunately, there is no way to automate this, other than setting everybody’s e-mail to plain text only or restricting everybody to the same e-mail client software, but we do not control everybody’s e-mail client programs.