Exemplo de SMTP
MTA remetente
Open conexão TCP, porta 25
HELO nome
MAIL FROM: remetente
RCPT TO: destinatário
DATA
... (linhas de texto)
...
.
QUIT
- MTA receptor (respostas)
220 xxxx (id, ready, data/hora)
250 (id, Hello, pleased to meet ..)
250 remetente - Sender OK
250 destinatário - Recipient OK
354 Enter mail, end with a “.” line
250 Mail accepted
221 Delivering mail