With a change in how we handle mail sending and using a transactional service over SMTP to do all mail sending for better deliverability we wanted to list a few free options that provide lots of emails at no cost.
At this time we don't have a method to do this, both login types use a different setup and has a different use structure. You can however move your resources between one account and the other by opening a container and clicking Transfer.
We have tried to make sharing really simple, and we are using the same system as container sharing using Tokens. To share your account to someone else you just need to visit settings and tap on Tokens to get started. You can also revoke Tokens from this menu.