Hello @gannicus, Welcome! According to @Igor Kurzin: in topic raised by @Katie_A Outlook email attachments with underscore extensions (.pdf for example as ."pd_") quote “Unfortunately, there is no automatic way for Kaspersky product to rename the attachments back. There are several other options though: 1. Visit the email server via web browser and download the attachments from the server. As the attachments were modified upon download and can remain unchanged on the server. This option might not be available for all email services. 2. Knowing the extentions (e.g. .pdf), you can rename them back manually after downloading the files, e.g.: .pd_ -> .pdf “ unquote Log a case with Kaspersky Technical Support, follow the template: include a detailed history, images & or video if relevant; the URL for this Community topic, Support may request a Traces & other data After submitting the case, you’ll receive an automated email with an INC+12digits reference number, then, normally, within 5 business days, a Kaspersky Technical Support human will communicate with you, also by email, you may continue to engage with the Kaspersky Technical Team via email or by updating the INC in your MyKaspersky account. Please let us know the outcome when it’s available? Also, check @Berny’s solution above, as a workaround, until Kaspersky Technical Support provide you with a solution. Thank you🙏 Flood🐳+🐋 Thank you for your response. How is it possible that Kaspersky was able to change the extension of my email attachments which I received many years ago? I mean how is it possible that the extensions changed not only in Outlook 365 but also on the ‘outlook server’? Could you provide an explanation for this please?