Incredimail is fine for 12 year olds like like bloating their emails with silly backgrounds and animations, but other than that it's junk and should never be considered a proper mail client.
Also, although you may not realise it, it adds animated adverts to the bottom of every mail you send, which hugely increases the chances of your mail being filtered out as spam by automated systems, and even if it doesn't it makes your mail look like it was sent by a child and annoys the recipient by making them download unneeded junk.
It's a gimmick more than a proper mail program.