which version of TB are you using ? TB v78 series uses RNP based OpenPGP builtin tool. TB v68 series uses GPG based OpenPGP external tool.

https://support.mozilla.org/en-US/kb/openpgp-thunderbird-howto-and-faq

and please also wait for other supporters to help you on this, if you need further help.

Where can I see which version I am using?

TB = Thunderbird version is shown here: in macOS : TB main menu > Firefox > About Firefox. in Windows/Linux : TB main menu > Help > About.

so if using v68 series TB or below, then, to find gpg version info: use commandline: gpg2 --verison gpg2 -h in macOS : /usr/local/gnupg-2.2/bin/gpg2 -h

i dont know how to get the RNP (RiboseNetPGP) version info from TB itself. but RNP websites showing their last version is v0.10.0 (August 2018) https://www.rnpgp.com/ https://github.com/rnpgp/rnp https://wiki.mozilla.org/Thunderbird:OpenPGP

Start Error Console : TB main menu > Developer Tools > Error Console. this may/will also show version info & other info when a RNP-OpenPGP or GPG/OpenPGP related operation is performed.

Ah thx, i use TB v78

I wanted to write with someone with encryption, send him my public key and I got his. But I can't read his encrypted mails.

Then the sender may not have encrypted the message to your public key.

In order for you to be able to send encrypted messages you'll have to set up your account for OpenPGP encryption, and import the recipient's public key into the OpenPGP Key Manager. You'll also have to 'accept' the recipients key before it can be used for encryption. See https://support.mozilla.org/en-US/kb/openpgp-thunderbird-howto-and-faq

I did all that, but i did not help. The sender encrypted the message to my public key. I guess my public key does not work for some reason, and therefore I can't read messages directed to that key.

do few-more secure-email TESTs with a person you know.

1. tell other side/person to create a new TEST based openpgp key , inside the TB software. create a new TEST key inside the TB software for yourself.

2. send the new pub-key to other side person via a non-encrypted email , this email can be signed. use a Text based/formatted plain email , not HTML based email. paste the entire armored-pub-key-code inside a new text-email & send that email as a text-email , send it to the other side. tell other side to do same.

3. when you receive new pub-key from other side, then, send one or two encrypted/(secure) email message(s), to other side/person, sender need to use their NEW key, and use the NEW pub-key of destination/receiver/other person.

4. again send one or two encrypted/(secure) email message(s), this time use your NEW openPGP key as sender AND use receiver's previous/OLD pub-key. tell other side to do also same : other side need to send you one or two ENCRYPTED emails by using his/her NEW key, and into your old/previous pub-key based email-address.

try to use same version of TB, as what the other side is using.

based on above TEST RESULT, you can figure out where the problem is, or go one step closer to find the problematic item ( or source of problem ).

if new encrypted/secure email comm fails , then obviously its TB's & PKI software's internal configuration issue.