Hello,
I have a problem with the e-mail forwarding to external addresses.
For this I have entered under the point eMail addresses Weiterletung to the external address.
This has been working for a relatively long time (~ 9 months), until about 6 weeks since then no external redirect has been made.
If an internal target is specified it works.
I can’t reproduce this… it works on my installations. Post a screenshot of your configuration.
Could you check also SPAM folder of external account: it can be there.
Post also mail packages version and mail log.
You can also try to solve this problem using Webtop rules.