UPDATE:As of June 1, 2020, Wayne RESA installed a hotfix for the Mass Email issue such that the error no longer appears for Chrome users of the version shown below.  

Wayne RESA has confirmed that recently introduced  Chrome Version 83.0.4103.61 causes issues in MISTAR’s Mass Email. An error will show when mass emails are attempted (most emails appear to go through, but still…).  Developers are working on a fix. For now, their suggested workaround if planning to use MiSTAR’s Mass Email function would be to use a different internet browser: Firefox, Edge or Safari.