Server change - glitch resolved
Server migration done, email disruption resolved (registration issue).
I moved from the old dedicated server to a slightly more powerful one.
The process was painless for existing users and I doubt anyone really noticed the transition except if using DNS servers that are not updated often enough.
Though, mail distribution from the redmine platform was disrupted for a while and no registration/notifications could therefore be done/sent.
This is now resolved, apologies for the inconvenience.