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I don't have access to writing any mail. When I press ' to open mail, it shows the icons from my guild
Do you use any add on which might interact with mail or how to handle guild in some way? I used MailR for a short time, but that add on made it impossible to delete mail with my standard keybinding, so I had to deactivate that add on. There are some add on also that is supposed to make life easier with guild (faster access to guild member for mail etc) instead of being forced to open up Guild Roster each time.
Try to turn off all your add on and see if you still have this problem and turn them on step by step to see when this will happen again!
If you don't use any add on at all, then I don't know what can have happened. Contact CS to get help there, if this thing still isn't solved.