http://www.cites.illinois.edu/security/idtheft/phishing/spoofing.html
This is most likely not the result of a "virus" (no viruses exist for OS X), or malware. But if you want to scan your Mail, you can use ClamXav. If it finds anything, it will probably only be some harmless Windows malware, which will not affect a Mac.
http://www.clamxav.com/download.php
Here is the current ClamX OS X malware catalog
daily.cvd not-OSX.Tored
daily.cvd OSX.Flashback-1
daily.cvd OSX.Flashback-3
daily.cvd OSX.Flashback-2
daily.cvd OSX.Flashback-4
daily.cvd Trojan.OSX.Miner
daily.cvd OSX.Defma
daily.cvd MacOSX.Revir-1
daily.cvd OSX.BlackHol
daily.cvd OSX.BlackHol-1
daily.cvd MacOSX.iMuler-1
daily.cvd Trojan.OSX.FlashBack.A
daily.cvd OSX.DevilRobber
main.cvd OSX.RSPlug
main.cvd Trojan.OSX.iservices.A
main.cvd Trojan.OSX.iservices.B
main.cvd OSX.DNSChanger.dmg
main.cvd OSX.DNSChanger.dmg-1
main.cvd Trojan.OSX.RSPlug.F.dmg
main.cvd Trojan.OSX.RSPlug.F.dmg-1
main.cvd Trojan.OSX.RSPlug.F.dmg-2
main.cvd Trojan.OSX.RSPlug.F.dmg-3
main.cvd Trojan.OSX.RSPlug.F.dmg-4
main.cvd Trojan.OSX.RSPlug.F.dmg-5
main.cvd Trojan.OSX.RSPlug.G.dmg
main.cvd Trojan.OSX.RSPlug.G
main.cvd Exploit.OSX.Safari
main.cvd Trojan.OSX.Cowhand
main.cvd Backdoor.OSX.BlackHole
main.cvd Trojan.Downloader.OSX
main.cvd OSX.Flashback
main.cvd Trojan.Downloader.OSX-1
main.cvd OSX.DNSChanger
main.cvd OSX.Trojan-2
main.cvd Trojan.OSX.Opener
main.cvd Trojan.OSX.RSPlug.C
main.cvd Trojan.OSX.RSPlug.D
main.cvd OSX.Tored
main.cvd OSX.RSPlug-2
main.cvd Trojan.OSX.OpinionSpy.B
main.cvd Trojan.OSX.OpinionSpy.A
main.cvd Trojan.OSX.MacDefender
main.cvd Trojan.OSX.MacDefender.B
main.cvd Trojan.OSX.MacDefender.C
main.cvd OSX.Defma-1
main.cvd OSX.Defma-2
main.cvd Trojan.OSX.MacBack
main.cvd Trojan-Downloader.OSX.Fav.A
main.cvd Trojan-Downloader.OSX.Fav.B