A very angry e-mail reply, often loaded with profanity or implied profanity. Can be either personal or business-related. Not to be confused with a flame, f-mails are issued as an expression of extreme dissatisfaction with a specific situation... where you eventually call somebody a monkeyfucker.
When my wireless card crapped out, Chris from Tech Support sent Tech Release 1.01b. When I e-mailed that Tech Release 1.01b didn't work, he sent Tech Release 1.01b. When I e-mailed him again that Tech Release 1.01b has nothing to do with my problem, he sent Tech Release 1.01b. I then f-mailed Chris, questioning his parentage and telling him to give the farm animals a rest.