Replies not saved in Sent folder

Outgoing new mail is saved in Sent folder, but replies are not. Just installed eM Client to try it, and am impressed, other than this problem. Any ideas?

Hi John,
I haven’t encountered this issue before, so could you please share more information so we can look into it? What account does it happen on, which mail provider and mail service do you use?

Best regards,
Olivia