If you have a Debian machine and emails appear to be coming from hostname @d1stkfactory, edit /etc/mailname and set this to your actual FQDN. Another instance where I found it locally is in /etc/exim4/update-exim4.conf.conf, which is almost certainly not read by my installation of Postfix (which does explicitly refer to /etc/mailname in one place).
This appeared on a machine running on DigitalOcean, so I presume “d” refers to DigitalOcean, and “factory” refers to their internal disk image building service. That’s just speculation though.
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via blog.vucica.net