You should state which Smalltalk you are using since there are different dialects and all have different ways of handling things like e-mail.
In Pharo, check out the class SMTPClient. There are class methods that have example methods showing how to send e-mails.
For VisualWorks, load the parcel NetClients and check out the classes MailMessage and SMTPClient.
Here's an example of code that sends an e-mail in VisualWorks:
(Net.SMTPClient host: Net.NetClient netSettings defaultOutgoingHost name)
user: Net.NetClient netSettings defaultOutgoingHost netUser;
send: (Net.MailMessage newTextPlain
subject: 'This is the subject';
from: 'my-email@gmail.com';
to: 'your-email@gmail.com';
text: 'This is the body';
yourself).