Struggled for a few minutes in order to get my email configuration of Simple Machine Forum based site. Finally the following settings seem to work. The settings have to be made to the following section of the Admin panel.

1) Admin -> Configuration -> Server Settings -> Feature Configuration dialog:

Mail type: “SMTP”
SMTP server: “localhost”
SMTP port: “25″
SMTP username: keep it blank
SMTP password: keep it blank
(confirm): keep it blank

2) Admin -> Configuration -> Server Settings -> Core Configuration dialog:

Webmaster Email Address:

It is advised though to use the “PHP default” instead of “SMTP” as the Mail type, because SMTP is suggested to be slow. But for some reason it is not working at the moment.

Tried to set up other my own web host’s SMTP server and also google’s SMTP server using the following settings but failed.

Mail type: “SMTP”
SMTP server: “smtp.gmail.com” (tried also smtp.google.com)
SMTP port : “465″ ( recommended port) or 587 or 25
SMTP username: my valid gmail mailbox for example “myaccount@gmail.com”
SMTP password: my gmail password
(confirm): my gmail password

Appreciate your suggestion if any.

source: http://myonecent.wordpress.com/2007/12/21/smf-email-configuration-settings/