Hi,
I've recently switched from Outlook 2007 to Mozilla Thunderbird, and I'm considering switching back. I'm not an IT person at all, and I admit that I don't know about the add-ons and full capabilities of Thunderbird yet (or of Outlook for that matter). But what I don't like about it is the following:

no calendar feature. I use a paper calendar, but I like to have a reference calendar to see dates and such. I did some research on Lightning and it got terrible reviews.

the signature is like in courier font and I can't seem to make it look nicer

annoying things like asking me if I want to send the message in plain text or HTML every time I send a message, and there's no "don't ask me again" box to click on.

I ask for your opinions on these two. I really like the concept of Open Source, and automatic updates and getting away from the Microsoft monopoly, but I'm not comfortable with it yet. What can it do that Outlook cannot, and vice-versa? What features are available that I am missing (I haven't added on anything yet).