[Exim] smtp after pop3 ?

Gd day,

i'm using exim 3.16.
i allow relay only for my local system.

is there a possibility to allow users which have a pop3 mailbox with my system to send mail also via our mailserver after they retrieved their mail from the pop3-mailbox ?

In other words - if i'm travelling, i can get easily my mail from the postbox - but to write, i always need to re-configure my computer for outgoing mail depending where i'm. It would be better if i can use always same configuration on my portable computer if the mailer yould accept my outgoing mail after having verified the pop3-mailbox passwords etc..

i have seen other mail software which allows a keyword "smtp_after_pop3 = xx minutes" (or something like that) which would allow the users to send mail after they have been authenticated by the pop3 password. Only thing i see is that the smtp remains then open for a couple of minutes (?)

Any suggestion ?

ciao
ANdreas