Users that are hosted on servers that are updated, are going to experience downtime for approx. 15 minutes within the maintenance window. Mail & Mobile Sync services will be totally unavailable during this time, including access to Webmail.
Mails received during the downtime will be queued on our mail servers and delivered once the server is available again. Mails sent during the downtime will be sent, but it is up to the mail client to move the mail to the sent folder once the server is available again.
If you experience any further trouble after the maintenance window has completed, please contact our chat support One.com/chat or write us at firstname.lastname@example.org