[exim] threads, mobile users and spammers (that is: self bcc…

I found three problems to be solved:
1. on many mobile devices there is not a big space for sent message,
also would be useful to have a copy also on main computer;
2. often one use divverent computer each one with is MUA, and most of
these use a different folder for sent maill
3. on my servers many times some users got their password stolen and
someone used it to send spam.
The solution would be to have a list of users that, in case someone
using SMTPA send messages using their username-password (irrespective of
sender/recipient), would automatically receive, as if their address
where in bcc:, a copy of the message.
Does someone have an idea what is the better way to accomplish this ?
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Leonardo Boselli