Intervals encodes all of its data in the UTF-8 format because of its language support. However, its an 8bit format that isn’t fully supported by mail software. We found that encoding our emails using the UTF-8 character set and 8bit encoding was working for some of our clients but not others. The culprit is the MTA servers that an email gets routed through. If any of those servers don’t support 8bit mime, the email gets garbled.

We found the solution was to retain the UTF-8 character set, but to encode both parts of the email, the text/plain and text/html parts, using quoted-printable. This ensures that the message is encoded into a 7bit format that can easily pass through any MTA. We are using the Pear Mail and Mail_mime packages to build and send the emails, which apparently, automatically mime encodes the UTF-8 headers.

No one seems certain as to how widely supported 8bit mime is on the majority of email servers. Our experience is the support is not enough. At least half of our outgoing emails were passing through a non-compliant MTA. 8bit is going to have to wait a while longer.