receiving signed mail show error at first opening

HI,

We are expirience with digital signed email from external source.

On first opening the mail we get a error message in the mail. "There were security errors withn this item. ..."

Further investigations show, that the complete certificate pth is valid and trusted. The only issue is, that the intermediate certificate is included in the certmgr from windows.

In outlook there is no issue shown, the path is automaticaly trusted.

The error is really confusing for our users. Is there the only way to import the intermediate certificate to the windows certmgr?

Best regards

Martin