eix -P misses packages when the virtual is specified with the category: $ eix --only-names -P virtual/mda mail-filter/maildrop mail-filter/procmail Whereas without the category, the list seems to be complete: $ eix --only-names -P mda mail-filter/maildrop mail-filter/procmail mail-mta/courier mail-mta/mini-qmail mail-mta/netqmail mail-mta/postfix mail-mta/qmail-ldap
The reason is that virtual/mda (because there is / inside) looks for the beginning of a string and not for a substring (like without /). The "true" bug is that eix considers PROVIDE as a single string and not as a vector of strings which is perhaps more reasonable. I added a corresponding patch to the eix svn trunk (>=eix-0.22.9).
app-portage/eix-0.22.9 is in the tree