[MlMt] don't understand the behaviour of my sent folders

[Paula Coelho]

hi there,

due to space limitations of my institutional email, i forward everything 
to a gmail account. i configured my gmail account to send messages as if 
it was from my institutional email.

so in MM, a message sent to my work email is received through gmail IMAP 
server (that's fine!) but replies through the institutional SMTP 
servers. i tried configuring my institution IMAP account with    gmail 
SMTP info, and then the sent message is duplicated, appearing in both my 
university account and gmail 'Sent Messages'.

what is the correct way to configure this? to send a message through 
gmail smtp (only) using my institutional email? i was going to fiddle 
with the option "Email Address(es)" in IMAP account setting but decided 
to ask first, before trying it by chance...

thx
paula