Can't set up Email Inbox : 'match error' - nothing in logs

I successfully deployed a brand new 4.8.1 instance and SMTP works for system emails.

Now I tried to configure the same email also as an inbox but I am getting “Match Error” in the Admin > Settings UI when trying to save my configuration. Nothing appears in the logs. I know it’s alpha but it seems this works for others.

Server Setup Information

  • Version of Rocket.Chat Server: 4.8.1
  • Operating System: Ubuntu 18.4
  • Deployment Method: Docker
  • Number of Running Instances: 1
  • DB Replicaset Oplog:
  • NodeJS Version:
  • MongoDB Version: 4.2.21
  • Proxy: NGINX
  • Firewalls involved:

SMTP & IMAP, both SSL/TLS on 993/587