Why doesn't this script work anymore? Last worked on Mikrotik 3.30 and stopped after that.

:local mailfrom "backup@XXXXXXXXXXXXX.com"
:local rcptto "backup@XXXXXXXXXXXXX.com"

/export file config

/tool e-mail send server=X.X.X.10 to=$rcptto from=$mailfrom subject=("{mtbackup} " . [/system identity get name] . " backup, " . [/system resource get version]) body="See attached file for configuration export." file=config.rsc

Since ROS 4.6:

email - user must enable tls explicitly

use:
/tool e-mail send tls=yes server=X.X.X.10 to=$rcptto from=$mailfrom subject=("{mtbackup} " . [/system identity get name] . " backup, " . [/system resource get version]) body="See attached file for configuration export." file=config.rsc

You may need to add a delay before emailing. It could be trying to send the file before the backup export is complete.