RE: Problem email client iPhone ios18.2

So yes, it must be a client issue, but it only seems to appear on dovecot imap servers. I've tested this on my private setup at home with Dovecot 2.3.19.1 from Debian 12 repository as well as at the company where we use Dovecot-ee 2.3.21-8 from the Open-xchange repository where the same happens.

How do you know it is specific to dovecot? You have tried also others? I think a lot use this cyrus not?