By default it should attempt to logon to Production. If you have however logged onto a Sandbox lately it may be worth checking the below settings:

1. 
2. Select Sign In With Salesforce
   1. 
3. Select ‘Use Custom Domain’
   1. 
4. Type in domino and select Continue
   1.    
5. Select ‘Log in with Domino Email
   1. 
6. Login with Domino Credentials and do any authentication required
   1. 
   2. 
   3. 

1. 
2. Select Sign In With Salesforce
   1. 
3. Select ‘Use Custom Domain’
   1. 
4. Type in domino--preprod or domino--deva and select Continue
   1.    
5. Select ‘Log in with Domino Email
   1. 
6. Login with Domino Credentials and do any authentication required
   1. 
   2. 
   3.