> like TTL, is there some kind of time to death for the sended mail for
> make it 'expire' and be deleted in the target mail server?

Not if it is already delivered to the user's mailbox on the the mail 
server.

But if still waiting to be delivered:

On sendmail, the configuration is confTO_QUEUERETURN (and a few similar 
ones) which defaults to timeout the message after five days. See 
cf/README.

For postfix, look at maximal_queue_lifetime configuration. See 
postconf(5) manual page. The default is also five days.

From the client side, you may want to look at RFC 2852, "Deliver By SMTP 
Service Extension". I have never knowingly used this. With sendmail, this 
is configured with confDELIVER_BY_MIN. I don't know how complete it is and 
probably is not very useful since most mail programs don't implement it. 
Does anyone know about or use RFC 2852 to comment on this?