Tagging of External Messages

Messages received from outside the CAU are marked with "X-CAU-External: YES" in message headers.

Also marked are messages with CAU From:-adresses that failed sender validation.

The header is not added for messages transmitted within the CAU and for messages from Geomar and UKSH if the messages supply sufficient authentication information (SPF, DKIM).

Tagging of Extermal Messages in the Webmailer "Roundcube"

Since June 22nd, 2025 external messages are automatically marked in Roundcube with [EXT] next to the sender address in the message list.

Tagging of external Messages in Mozilla Thunderbird

Direct use of the message header in Thunderbird is not possible. However, Mozilla Thunderbird maps its internal "Tags" to named IMAP flags.

Using this approach it is possible to have external mails automatically signed to a category. This can be done in two steps

Step 1: Making the Header into an IMAP flag

Step 1: Log into the Webmailer "Roundcube" an und switch to settings (gear icon)

Step 2: Select "Filters" and then "create" to the right to create an new filter rule in the current filterset.

Step 3:

Under Rules select "..." and enter "X-CAU-External" as the header name. In the value field enter "YES". The rule should then read "X-CAU-External contains YES"

Step 4: Save the new rule

Step 2: Use of the IMAP-Flag in Mozilla Thunderbird

Mozilla Thunderbird translates its  "Tags" internal to IMAP-Flags. The pre-Configured Tags are mapped to numbered IMAP-Flags, but new tags are mapped to named IMAP-Flags with the same name. Thus you can make the IMAP flags visible by simply creating a new tag "External"

Step 1: In Thunderbird, click on an arbitrary message in the message list.

Step 2: In the context menu select  "Tag" and then "New Tag"

Step 3: Create a new tag "External" (Note case is important) and select color of your chosing.

Messages from external senders should now be marked and colored as selected.