Postfix: how to identify the mail client in which the letter is composed?

Question

linux

Good afternoon. I add signatures to outgoing messages using altermime. Some employees use Outlook, some use Thunderbird. Signature must be added to Outlook letters in KOI8-R encoding, to letters from Thunderbird - in UTF-8. How to uniquely identify the client from which the letter was sent (by analyzing the source code of the letter)?
I noticed that emails sent from Thunderbird have a line like

User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.2.2

and emails from Outlook

X-Mailer: Microsoft Outlook 14.0

It would seem that you can crack this line and understand where the letter was sent from. But. If a user from his Outlook REPLYS to an email sent from Thunderbird, the outgoing email will contain both attributes at once.

Answer 1

Use the utility to determine the encoding of the letter, as I understand this is your problem?