In my install of Alfresco Community 5.1, in the records management site when I try to complete an email (.eml) record that has a MIME of message/rfc822 I get a dialog that tells me to enter metadata for the file to complete the record. I fill out all available fields for the metadata and when I try to continue to complete the record I continue to get the dialog asking for me to enter metadata for the file.
This sounds like it might be related to (or the same as) RM-5008. That ticket includes a workaround of configuring RM to allow completion of the records with missing mandatory properties - i.e. setting rm.completerecord.mandatorypropertiescheck.enabled=true
We hope to fix this issue in the near future, but it has been de-prioritized due to the workaround.