My exim server is configured to reject potentially unsafe attachments. When that is attempted, an exim log entry is appended such as: 2022-08-25 22:23:32 1oRRoH-005RxB-BP cancelled by system filter: This message has been rejected because it has a potentially executable attachment "example.eml" This form of attachment has been used by recent viruses or other malware. If you meant to send this file then please package it up as a zip file and resend it. Thunderbird gives me zero real-time indication that it was rejected and stores it in the Sent folder. I'm prone to forget that certain attachments are not allowed, plus there may be any number of other possible reasons for rejections. The problem is that I have no awareness that such emails have not been delivered until days later -- if I'm lucky and/or diligent enough to inquire -- when the recipient informs me they never received it. Is there any way to enable real-time indication of when an outgoing message is rejected and keep the message in the Drafts folder? Thunderbird 91.11.0 (64-bit) for Linux (Pop!_OS 22.04 LTS)