When sending email reports the From: attribute is not specified.
Some SMTP servers reject with a "From address not verified" error.
Please add "From" attribute when sending reports by email.
Keywords: email, reports
Are you using Piwik 1.7?
The From: should either be "Piwik reports" (if you don't use custom logo) or "web analytics report" if you use a custom logo.
Works for me in 1.7..