I had contacted TM about this and requested they remove the block until they find a more suitable solution with sufficient notice to their customers. They have unblocked port 25 yesterday. Please try with your old settings and it should work.

They also mentioned using port 587 as an alternative. Many mailservers use port 26 as an alternative or can be configured to use a different port. Actually using an alternative port is not a solution from TM, it is up to the mailserver administrator to set it up. As long as TM does not block any ports that are going to be used.