Email Spoofing

[dirtydog]

This might amuse some of you, all these sites do is pretend to be whatever you want them to be, ie you can pretend you are Bangkok Bank and give account closure notices, basically it justs spoofs the email address.

anonymousmailsender.popatrz.pl/
deadfake.com/Send.aspx
anonymailer.net/

Here's one I done for Bill Clintons girlfriend

[Baby Farts]

I guess accounting will have to give me that raise I needed so bad since the email to them came from the boss. 

[yzberslick]

You can use things like DKIM or SPF in your domain. It means you are stating that you 'authorize' mail via server X. These measures increase the 'reputation' of sending mail servers for your domain.
But the verification checks are made on the recipient. No one really blocks based on SPF or DKIM since email is 'open' in that sense that you can send a 'valid' email from anywhere.
It's up to to the receiving email server to determine if they want to accept and forward on a sending email.