No Connection from Smartphone to Roundcube via Synology

[stefanghh]

Hello from Hamburg,

Whether you have an idea. I've run out of them.

Following. Yesterday I migrated from a DS218+ to a DS918+. Backed up and restored settings using Hyper Backup via hard drive migration. It was largely unproblematic and everything works again - except for external access to the mail station via Roundcube. I've attached a screenshot.

What works:
- I can access Roundcube locally, also via local Outlook (i.e. from the PC)
- Roundcube receives emails.
- I can also send emails from my smartphone.

What doesn't work
- See screenshot (Connection with E-Mail Server Cannot connect to email server to verify account information. No response from server)

DDNS has been tested and shows normal ports have been adopted. I guess it's some kind of setting but I can't figure it out. Especially since I didn't change anything. Thanks for the help