In a decision dated 9 March 2022 (docket no. 4 W 119/20), the Hamm Appellate Court (OLG Hamm) opined that a warning letter that is merely sent as a file attachment to an e-mail is generally only received if and when the e-mail recipient has actually opened the file attachment. 

The court stated that in view of the fact that there is a general warning against opening attachments from e-mails from unknown senders due to the risk of viruses, the recipient cannot be required to open the file attachment in such a case. According to the court it was therefore irrelevant whether the e-mails in question were received at all in the regular e-mail inbox or the spam folder of the defendant. By submitting a respective affidavit, the defendant has in any case made it credible that he did not become aware of the two e-mails from the plaintiff's attorney - who was unknown to him - and accordingly did not open the file attachment with the warning letter.

In consequence, it is advisable to include the contents of warning letters directly in an email and not only in email attachments.

OLG Hamm decision (only available in German)