My sieve mail filter does not work

Problems with filter rules

If your filter rules are not working as expected, there may be several reasons.
If the outcome of the configured filters differs from your expectation, it is usually because the filters were misconfigured or because multiple filters are interfering with each other.

Note: We cannot provide support for the individual configuration of your filters.
Disable all filters and then reactivate them one by one to identify where the error occurs.

Linked / external mailboxes

If you are retrieving mail from external mailboxes that you have linked in mailbox, the Sieve filters or filter rules are not applied to these mailboxes. This applies both to your own filters and to our spam and virus filters.

The reason is that Sieve filters only apply to mail that is “normally” delivered to your mailbox address via SMTP. Mail from linked external mailboxes is not delivered into your mailbox but merely displayed in your account – similar to how you work with mail locally using IMAP.

To apply your filters to these messages as well, you would need to either forward them from your external account to your mailbox account or retrieve the mail from there using POP3.