Vlk,
Here's a very interesting observation:
1. IMF updates are issued by Microsoft only two times per month.
2. Before the Avast 4.8.1049 upgrade, the ID 7513 events occurred only a few times each month.
3. After the Avast 4.8.1049 upgrade, the ID 7513 events are occurring every two hours almost exactly (plus or minus a few minutes each time).
I suspect, therefore, that Avast 4.8.1049 is somehow causing the ID 7513 events every two hours, perhaps by restarting the SMTP service. In other words, the ID 7513 events are a symptom of a problem in Avast which occurs every two hours, not the cause of the problem.
What does Avast do every two hours, plus or minus a few minutes? Does Avast attempt a VPS update? Is the SMTP service involved?