Forwarding of messages with attachments seemingly randomly fail with the following Send Message Error Sending of the message failed. There was an error attaching <filename>. Please check that you have access to the file. The workaround is to discard the email and start the forwarding process again and it works OK. This is an error that has been happening for us for about a month first reported internally the 14th October. We're using Thunderbird 91.3.0 (64-bit) on Windows Server 2019 Standard - Version 1809 OS build 17763.2300 Any help would be appreciated as this is rather annoying. Thanks in advance.