I had a somewhat similar experience, and I determined it was helpful to make some unique message subject lines and "from" entries for each type of alert and message my Solarwinds systems might send out.
I ended up editing each alert's "Action" to provide more information about the specific alert that fired. This also included the Alert-cleared / Recovered actions.
Then I adjusted the e-mail / pager settings to provide the name of the specific SW poller/server/instance that sent the message, so it would be easier to troubleshoot messages by knowing the source server.
It was a little time consuming, but it paid off handsomely.
If this isn't what you're looking for, you might be able to learn more about the message sent by going to the Message Center: https://your-npm-server/orion/netperfmon/orionmessages.aspx and then filtering or searching for events or messages that happened at the date/time in question:
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Fortunately, the admin for our environment before me was kind enough to create custom alerts with their own email subjects to detail what they are for (server name, error, issue, drive letter, etc.)
I looked through our alerts and messages and we didn't have any sent out around that time. The only thing I can see that went out anywhere near that time was the Alert Central Weekly Reports based on my email box.