In every version of it Outlook I've used, it stands out as being terrible at dealing with email in general (aside from the various exploits just from opening malformed emails). It's got rules that cancel themselves because the computer just woke from sleep and isn't connected to the internet (and therefore the rules are "invalid") to having a hojillion different sources of email addresses, none of them configurable or editable (Seriously, why can't I fix a misspelling in an email once it's been saved wherever the hell it gets saved?). Autocompletion of email addresses is a complete clusterfuck. I had to delete a customer from my contact list completely and start over because her email address changed and when I edited her contact, her record refused to come up when I'm sending an email (Doesn't come up when I type, doesn't come up in the contact list when I press the "To" button, but if I write her email by hand and choose "Look Up Outlook Contact" bam there she is complete with name and company information)
If it weren't for Exchange, I'd have ditched this shit long ago. Sadly, it's still the best I've got at dealing with scheduling meetings (at least as long as they're in our own time zone).