What I did
emerge --unmerge mta
# To get rid of ssmtp
# After this point ssmtp and procmail were installed (but not sendmail
emerge --unmerge ssmtp
# To get rid of ssmtp so I could install sendmail
# This finally worked
According to peitolm
"sendmail provides virtual/mta, but if you have mbox in USE, then it pulls in
procmail. which requires virtual/mta but at the dependancy checking, I think it
doesn't realise sendmail will provide it"
I haven't put mbox into the USE, so I'm assuming this is a default.
This is the third machine I've had this happen on.
*** This bug has been marked as a duplicate of 1343 ***