If you can see 'reply' and 'forward', then right-click on that toolbar and select 'customize.' A window will open and the write icon should be visible. Highlight it and drag it up to the toolbar.

Davids fix does not show the write icon

The reply forward icons only shows up when I click on a email in my inbox not at the top my address book is also gone. At the top it has unread, stared, contact, tags, attachments

Found a fix that works for me. Click view, then click tool bars check mark mail toolbar. Some how mine got uncheck.