I just noticed that if I check the SENT folder, some of the emails I sent have this text in the '''body '''part. "This is a multi-part message in MIME format. --------------nIbrxwPoa2BBm60hwjHS8H3t Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit [HERE THE CONTENT OF THE EMAIL I SENT]" I'm wondering if they are sent like that, what the receiver will see and if there is a way to prevent it. The email account is using IMAP and as far as I know it happen just to that specific email account. The emails are sent using Thunderbird. I'm using the latest version of Windows on a laptop. I'm using the following Thunderbird extensions (latest versions): - Compact Headers - Send Later - Mailmindr - Quicktext