After few days until last upgrade, yesterday I've received from Live update service the new FP3 for IMSMO.
This FP introduce some fixes and corrections and finally, the introduce the ability to save the account password.
To find this new setting , go to Control Panel -> Mail -> email account setting
double click on the IMSMO account, then after click nexdt you will be prompted for username and password, then you will be asked about the save:
Read this page to get the complete list of the fixes introduced with this FP 3.