Unable to force S/MIME encryption method

[Buttered Toast]

I have some contacts who can only decrypt 3DES and Enigmail encrypts with AES128 per default.

I've read in the FAQ, that I can use --cipher-algo to force the usage of a specific algorithm. Now, I've configured this, when sending a new mail in Enigmail, Preferences, Send Options..., Advanced (Expert Setting/Menu), Additional parameters for GnuPG: --cipher-algo 3DES.

I've also check with gpg.exe --version and 3DES is available and supported, but the mail is encrypted using AES128. Using gpg (GnuPG) 2.2.19, libgcrypt 1.8.5 on Windows 10 with Thunderbird 68.4.2 (32-bit) and Enigmail 2.1.5.

How do I correctly force the use of said encryption algorithm?

[Patrick Brunschwig]

Enigmail does not set the cipher-algo on its own. I don't know what is required to make GnuPG use a specific algorithm. You better ask the gnupg-users mailing list for support for this.

[Buttered Toast]

The enigmail FAQ states the following (https://enigmail.net/index.php/en/user-manual/handbook-faq)

Which symmetric ciphers does Enigmail use?
...
Note that you can force usage of a specific symmetric algorithm by using the GnuPG option --cipher-algo, but this is not recommended; this option can easily break things and is intended for debug purposes only.