Well, today's your lucky day. Because it takes a program called telnet to send spoofed emails. For instance, you could connect to mx1.hotmail.com (mail exchange server 1) on port 25 and then type this:
helo (not a typing error)[enter]
(server replies saying "Hello,
you@your.host or IP")
mail from:
spoof@this.com (email to send from) [enter]
(reply: 250 OK)
rcpt to:
this-is-the@destination.email.com (email to send to) [email]
(reply: 250 OK)
data (typing the data line tells the email server you're ready to start the message information.) [enter]
subject: blah blah (subject, if there is one. if not, skip this step) [enter] [enter]
this is the message, w00t w00t. (type the message after pressing enter twice after subject, then press enter twice after the message.)[enter] [enter]
. (yes, just one period, then press enter.) [enter]
Now, the email server should say something about the mail being queued.
However, if you really want a mailer application, then go
here, but be careful. I used that site alot when i was a script kiddie and alot of the files on there are bound with a virus, so scan the program before using it. Also, don't use that website too much, it turns you into a huge ass script kiddie.