The Message-Id field uses only the hostname, not the FQDN. The hostname itself is very likely not unique (think of all that OEMCOMPUTER XP machines), so the FQDN should be used instead. Reproducible: Always
For the moment we use : "QHostInfo::localHostName()" which returns a value all the time. but try to get all information about fqdn will take time and not sure that it's really possible. Don't know a method to do it easily.
QHostInfo::localDomainName()? Btw, I think this is the code in messagecomposer/job/skeletonmessagejob.cpp. When the FQDN getting fails it shows a message that it will use localhost.localdomain, but instead it uses local.domain.
QHostInfo::localDomainName() I tested it, it returns QString() for me.
This bug has only been reported for versions before 4.14, which have been unsupported for at least two years now. Can anyone tell if this bug still present? If noone confirms this bug for a Framework-based version of kmail2 (version 5.0 or later, as part of KDE Applications 15.12 or later), it gets closed in about three months.
Just as announced in my last comment, I close this bug. If you encounter it again in a recent version (at least 5.0 aka 15.08), please open a new one unless it already exists. Thank you for all your input.