Email on SQL 2005 and later is an asynchronous process. Even with a wrong address, that won't stop a job, it just enters an error in a log table in msdb.
A stop job request has to initiate from a sys admin, or from software with that kind of privileges. Some server monitoring software, and some antivirus software, can stop a job mid-flight, but the usual culprit is someone doing something like cancelling the job or killing the service.
Have you checked the Windows logs?
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