At the moment there's no portable version of Mailbird available, but it is something which we may consider in future.
While our development team is working on delivering this functionality, we would like to count on your support for it so that it is implemented even sooner.
Simply click on the link below to let us know that you would like to be able to have a Portable version of Mailbird:
While we are sorry that this is not possible at present, rest assured that every vote counts as part of our development roadmap, so we appreciate the time you will take to vote for these features.