GMass is written mostly in C# and JavaScript, and the C# backend makes heavy use of a popular email parsing component called MimeKit. In face, MimeKit, has become so popular that Microsoft is now recommending that developers use it as the standard instead of Microsoft's own SmtpClient library.

Over the weekend, we updated some of the software components that GMass is built on in preparation for a big feature launch, and in doing so, we updated MimeKit from version 1.12 to the latest release 1.18. That upgrade unfortunately broke some of our email address validation code, and many users saw a "token offset" error as a result.