Incredimail™, although a very 'pretty' email program is in fact very intrusive indeed.
It is common knowledge that the operators of Incredimail™ are in Israel, and because of that they can do alll sorts of things that would be considered as an invasion of privacy in many countries (including Australia).
When using Incredimail™, any email that you send is only 'relayed' by your ISP (Optusnet) to the Incredimail Server; then, Incredimail 'send' the email (but not before they have recorded the sender and receiver's email addresses and the email contents in its database, for on 'selling' to advertisers.)
In view of this, perhaps Optusnet (I used to use them as my ISP until recently) have 'censored' Incredimail's Server IP address and classified it as SPAM.
One way to check this is to open the Optusnet Desktop Service Centre that came with the installation of your (presumably) D-Link DSL-302G Modem (if you are on Broadband), and then sign in to your mum's Web Mail Account and see if the Spam Filter is On
...if it is On
; then, chances are that the Incredimail traffic has been Blocked
as SPAM for the reasons I have said.
So if your mum still insists on using Incredimail, you can switch Off
Optusnet's email SPAM filter; however, this will not
prevent all kinds of SPAM etc from being sent to her.
My sincerest advice is to tell your mum to forget Incredimail and go on to Google™ and search for the free smilies etc. that are available for emails, and use them and the Optusnet email through Outlook Express™.
If you need some information about free email attachment type programs, just PM me and I'll send you some details of ones that are known to be safe to use.