If you are scanning your emails with your Anti Virus the disable that option by
uninstalling your AV and then re-installing it without the mail
integration(scanning). The reason to do this above is that by only disabling the
scanning option does not take hold on some AV suites. Since we do not know which AV
you are using then hence the above.
Also see the following http://thundercloud.net/infoave/tutorials/email-scanning/index.htm
