Clicking on the URL containing http://mlbtlr.com is SAFE.
You see the http://mlbtlr.com in your email because the sender of the email is using Mailbutler. Mailbutler is an email extension which adds multiple features to the user's mailbox.
One of the features of Mailbutler is Link Tracking. The http://mlbtlr.com URL allows the sender to make sure that the recipient received and opened their link.
This is only a temporary redirect. When you click a link in a message with Link Tracking, the mlbtlr.com page loads for a second to register a link being opened, and then you are taken to the original page linked in the email.
No personal data is being stored by Mailbutler
If you have any questions, please contact firstname.lastname@example.org.