First
set up your own Twtxt feed on your own domain.
Then create a twtxt message as, by appending a line to your own twtxt.txt file with the following content:
@<johanbove https://johanbove.info/twtxt.txt> hello!
And then upload your twtxt.txt file to your own server.
Now you send me a ping of your existence by opening my twtxt.txt file from your own Twtxt instance. You could use curl for this too. With a bit of luck I will see the entry show up in my server logs.
You can reference which twt message to reply to by using the corresponding Twthash code. This is the string underneath the date next to each of the messages. You can take this string and then start your reply with it, like this:
(#klyldsq) @<johanbove https://johanbove.info/twtxt.txt> Your reply to my message with the hash klyldsq
If all of this seems too complicated, then I am of course happy to also receive e-mail at hello@johanbove.info. You could still use the Twthash in your subject line.