I find it vaguely amusing that the vitriolic People for the American Way e-mail I received today was flagged by Thunderbird. “Thunderbird thinks this is a possible scam.”
It was probably because of a mismatch between the mailing address and return domain, or where the images were hosted, or something, but it was kind of funny.
(And I suspect most political action e-mails would be likely to have the same warning, so don’t consider this a partisan slur.)