I have just purchased a handful of Runbox accounts to migrate our email from Tuffmail, who have provided us with a superb service for well over a decade—with only a single downtime lasting just a few hours in the last 15 years. So far, everything seems to work reasonably well on Runbox. I have already shared a few suggestions and improvement ideas, hopefully not too many. 
Many thanks to Dave and Liz for their patient and prompt Runbox support.
However, I would like to have more certainty about service reliability before I migrate our most important mailboxes from Office 365 Exchange. I note that there was an issue last year described in Am I the only one experiencing IMAP (and some other) RB performance problems? - #17 by Geir in which @Geir wrote that:
We are considering options for architectures that provide greater distribution and isolation, as well as redundancy. First of all we need to resolve the most urgent issue at hand, which involved migrating data from one of our storage units to a new replacement server.
May I respectfully ask if Runbox have implemented the new architecture? While my business could cope with a mail outage lasting a few hours to a day, anything lasting several days, especially mid-week, or even worse, any negative impact on our domain reputation and deliverability would be quite negative. Thank you for your openness.