
If you don't need the new features, then we recommend you do not upgrade Notes support: once upgraded, you can't go back. These extra features are not available if you are using IMAP based Notes through Fastmail. Warning: The new Notes features are available to OS X 10.11/iOS 9 users only if you are using Apple's upgraded Notes with iCloud support. If you do this, Mail.app will let you choose which one you would like to use each time you compose a message. You can also enter multiple email addresses, separated by a comma. Instead, in the Email Address field, replace your Fastmail username with the address you wish to use instead.
In MacOS prior to 10.11 (El Capitan), there is no aliases option. Use the Edit Aliases option to add, delete or change your list of alternate addresses. Use the Aliases pop up menu to access your alternate addresses.
Select your Fastmail account on the left. Go to Mail → Preferences and select the Accounts tab. To use a different email address to your Fastmail username: Looking for instructions on how to manually set up Mail, Calendar, or Contacts? If you open the Profiles tool, you'll see a single entry for your Fastmail accounts. If you open your internet accounts list on your Mac, you'll see your accounts listed there. Examine the profile ("Show Profile") and make sure it has access to which of email, contacts (CardDAV) and calendars (CalDAV) you require, and install it if it's correct. This will download the configuration file to set everything up on your Mac automatically.
Click the link that says Open this configuration file.
The following screen will show information about the app password that has been created. Choose what sort of access this password requires. Give your app password a name to indicate which device and app this password is for. Unlock it with your password, then click Manage. Log in to the Fastmail web interface on your Mac and go to the Password & Security screen. The easiest way to set up a Mac is to use our automatic setup tool which will take care of the app password entry for you. If you use your normal password on an external account, syncing won't work and you will see a password error. Mac Mail, Calendar and Contacts apps need their own app password to access your information.