This pesky little issue prevented me in adding a lot of links to wallabag, but as it turns out, the fix is really simple.
Switching mailserver with lots of active users isn't an easy task. First you need to copy the mails to the new server and then get all the users to change mailserver settings at the same time to switch to the new server.
Change SSH client settings to enable SSH logins to older SSH servers or Mikrotik routers
Adding new disks to a LSI controller, creating a new VD and extending an existing LVM volume group
Having to move ~ 180 Mail accounts from an older IMAP server to Zimbra (open source version) I though I would document the process if anyone else finds themself in this situation.