Sent messages sent from phone not linked to conversations

When I answer an email with eM Client, it is linked to the email forming a conversation.
But if I answer an email with an android app, the sent email is not linked to the received one, and there is no conversation formed. However, the sent message does appear in sent folder.
How can I fix this?
Thanks for your help

I have this exact same issue. On my phone I currently use the Samsung email app, and it does not include the header references in the sent message.

This is something you will need to discuss with the app author, as it is a fault or omission in their code.