Proprietary or non-standard SMTP AUTH mechanisms

Are there any known proprietary or other non-standard SMTP AUTH mechanisms that 
deviate from the syntax specified un RFC4954?

For example, is there an unofficial SMTP AUTH mechanism that allows unencoded 
binary data in the challenges or responses?  A vendor controlling both the 
client and the server could get away with something like that, but something 
standards-based analyzing that traffic might be confused by it.

Thanks,
-MSK