If an email is sent from an account with a comma in the username, the "From" email header is malformed. It appears as:
From: <part of name before the comma>@localhost.localdomain, <part of name after the comma> <correct email>
So if a username is: "Foo, Bar" with email address foo@bar.com it would be sent as from:
Foo@localhost.localdomain, Bar <foo@bar.com>
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Severity: normal